1 Extending the Artificial Habitability Zone to Pluto? Payton E. Pearson III B.S. Electrical Engineering, 2LT USAF Laughlin Air Force Base [email protected]
Abstract—This paper—the second in a series of papers expanding variation in distance of Pluto leads to equitably large upon this topic—seeks to show how the habitability of various variations in surface temperature. The surface temperature of celestial bodies throughout the universe can be engineered, Pluto can be derived using the equilibrium temperature nearly regardless of distance from the host star. An atmosphere equation, assuming that Pluto is currently in temperature is hypothetically engineered and shown to be theoretically viable equilibrium [1]. on the dwarf planet, Pluto. This hypothetical atmosphere is engineered to be 280 Kelvin at the surface of Pluto, with half the atmospheric pressure of Earth’s surface (~506 mbar). Nothing √ (1) else is significantly changed; though an explanation of possible modification of orbital dynamics is posited, placing Pluto in a 26 390,000 kilometre orbit around a previously designed Where Lo is solar luminosity (3.839x10 watts), is the hypothetical planet, PH. This paper will refer back to the albedo of the celestial body in question, is the Stefan- original artificial habitability paper for certain ideas. As with Boltzmann constant (5.670373x10-8 w/m2K4), and R is the the last paper, the hope in creating this series is to galvanize the AU distance in meters from the Sun of the celestial body. Using interest of prospective scientists, and stimulate discussion on the matter of astrogeophysical engineering. Pluto’s minimum distance from the Sun and its albedo of 0.55, Pluto’s surface temperature reaches a maximum of:
Keywords— Pluto, magnetosphere, habitability zone, equilibrium temperature, hypsometric equation, Universal Law of Gravitation, solar flux, atmosphere, atmospheric mass, √ √ [ ] sputtering, orbital dynamics.
I. INTRODUCTION So, what is it that makes a celestial body naturally habitable? Of course, temperature is a key factor in that the surface The same calculation used with Pluto’s maximum temperatures of a celestial body must be adequate to support distance from the Sun reveals a minimum surface complex life in some form. Also, atmospheric pressure at the temperature of Pluto of 32.6324 Kelvin. This implies a surface is vital, because most organisms require some form of temperature variation of 41.8883 – 32.6324 = 9.2559 Kelvin, inward pressure in order to sustain physiological equilibrium. or approximately 16.66 degrees Fahrenheit. This means In addition to this, metabolism requires some form of that while there would be significant swings in the average sustenance from an atmosphere to allow for more complex life surface temperature of Pluto, these swings would not be so to eventually develop. Once more, the lowest tropic levels of drastic as to render Pluto completely uninhabitable. So far, life on Earth oftentimes utilize some form of photosynthesis in Earth’s astronomers’ relatively limited understanding of for metabolic purposes as well, though some extremophiles the universe, exoplanets have been discovered that have have been known to utilize chemical processes of Earth temperature swings of several thousands of degrees instead. Fahrenheit, going from -150 degrees to 850 degrees Nevertheless, taking into consideration these basic Fahrenheit over the course of 30 months [2]. Earth components to developing complex life on a celestial body, experiences relatively constant temperatures, as its closest the dwarf planet Pluto, which orbits the Sun at a variable approach to the Sun puts it just shy of 90 million miles away, distance between 4 and 7 billion kilometres depending on and its farthest distance puts Earth at about 95 million miles whether it is at apogee or perigee, the notion of rendering such away from the Sun. This stability is a major contributing a distant, cold, dark celestial body habitable sounds absurd. factor to the development of the complex ecosystems This paper will show that it may not be as absurd as some present on Earth today. think. But a 16.66 degree variation is not unacceptable, especially considering that humanity will have the ability to II. BASIC PARAMETERS OF PLUTO engineer the biosphere of Pluto from scratch. Seeing as how
this is the case, temperature variations will nevertheless be a The dwarf planet Pluto is an icy world that orbits the Sun at crucial component to understand in order to attain a maximum distance of 7.311 billion kilometres and a environmental stability. minimum distance of 4.437 billion kilometres. This large 2 Another important component to the engineering of the atmosphere in kg of atoms, and g is the gravitational Pluto’s atmosphere is the extremely low gravity when acceleration at the surface. Pluto’s atmosphere would more compared to Earth. Pluto has a gravitational acceleration at than likely be composed of very similar elements to that of the its surface of 0.658 m/s2. This is a mere 6.71% of the Earth. This is because the surface of Pluto is comprised in gravitational acceleration at the surface of Earth. With such large part of water ice as well as N2 ice. This greatly a low gravitational acceleration, a proposed atmosphere for simplifies the equations of the atmospheric scale height, as the Pluto of any significant mass would be exceptionally same atmospheric weight that is used for Earth can be distended compared to that of the Earth. These calculations assumed for Pluto [4]. In this case, the atmospheric weight is will be elaborated upon later in this paper. But beyond this, 4.76x10-26 kg [4]. An average surface temperature of 36 there comes the issue of atmospheric sputtering due to solar Kelvin will be used for this hypothetical example. wind, a mechanism that caused the atmosphere of Mars to dissipate from approximately the same surface pressure of
Earth to what it is today over the course of 10 million years [3]. The design parameters that Pluto will be engineered to Compare this to a scale height for Earth’s atmosphere of have are as follows: roughly 8.7 kilometres. This may not seem like a very drastic difference, but this alone can cause the atmosphere to be Atmospheric Pressure of PH = 0.506 bar roughly 1.826 times as distended, for an atmospheric Desired Surface Temperature = 280 Kelvin thickness of 182.6 kilometres based upon the Karman Line of Earth. This approaches 16% of the overall radius of Pluto. No other bulk parameters of Pluto will be changed for the Once more, this does not even take into consideration the fact purposes of this design. that this design is intended to increase the surface temperature of Pluto to 280 Kelvin. As such, the scale height of such an atmosphere would be 123.6 kilometres. This would potentially increase the thickness of a Plutonian atmosphere to 1421 kilometres, or roughly 120% the radius of Pluto itself. As can be seen clearly, this would produce an atmosphere that is utterly gigantic by comparison to the size of Pluto. But is this truly a problem? Before this question can be answered, a more accurate estimate of the thickness of Pluto’s atmosphere must be found. We will use the hypsometric equation under the engineering assumptions of temperature and surface pressure to find the overall thickness of the atmosphere. The hypsometric equation is as follows [4]:
̅ ( ) (3)
Where R is the specific gas constant of the atmosphere. Fig. 1 This is an artist’s interpretation of how the surface of Pluto might look currently. This would change drastically with the introduction of a liveable Assuming it is identical to the Earth, it is 287.058 J/kgK. ̅ is atmosphere. the mean temperature of a specified atmospheric layer. As was done in a previous paper [5], we will use the Earth’s III. PRODUCING THE ATMOSPHERE FOR PLUTO atmospheric temperature profile in order to find the The most difficult hurdle to overcome when producing an temperatures of the respective layers of Pluto’s hypothetical atmosphere for the dwarf planet is the extremely low gravity atmosphere. Also, g is the gravitational acceleration of the at the surface. This would cause any atmosphere that would celestial body with respect to distance above the surface. P1 be produced to be exceptionally distended and possibly and P2 are the pressures at the top and the bottom of the layer unstable, perhaps becoming several dozens of times the height of atmosphere in question. of that of Earth’s atmosphere as defined by the Karman Line. This is evidenced through the fact that Pluto’s atmospheric scale height is much greater than Earth. It is calculated as follows [4]:
(2)
Where k is the Boltzmann constant (1.38x10-23 J/degree), T is average surface temperature in Kelvin, m is average mass of 3 layer in question, the temperatures of each layer of atmosphere using the average area theorem are [6]
̅
̅
̅
̅
̅
As was done in the previous paper in this series [5], the termination point of Pluto’s atmosphere is based upon the pressure at Earth’s Karman Line, not upon the derived Fig. 2 Earth’s temperature and composition profile as a function of elevation above sea level. As can be seen clearly, the temperature profile does not Karman Line of Pluto itself, which would be much higher. follow a simple, linear path, but instead is a conglomeration of discrete Other methods can easily be proposed, but this method proves functions. to be adequate for the endeavour, and simplest. The It is important to note that if Pluto were heated up to atmospheric temperature profile is thus as follows: terrestrial temperatures, it would likely take the form of a giant water ball, also known as a water world. This is because Layer P1 (mbar) P2 (mbar) Tmean (K) a large proportion of the overall mass of Pluto is in fact H1 506.000 82.552 245 comprised of water ice, in particular the surface and upper H2 82.552 43.933 210 mantle. Once more, a significant layer of frozen nitrogen lies H3 43.933 5.0412 213 on the very topmost portion of Pluto’s icy crust. The H4 5.0412 0.3797 239 ramifications of the presence of this nitrogen ice will be H5 0.3797 0.1533 252 elaborated upon later. Table 1 This is a more organized view of the mean temperatures with respect to the pressure layers. It is important to note that with a much lower equilibrium temperature, the drop off in temperatures past the troposphere would likely be much more dramatic. It must be emphasized that this is merely an engineering approximation. To lend credibility to this approximation however, Titan does not experience such an exponential drop- off in temperature with respect to height until far beyond the Karman Line [7]. Now that the mean temperatures of each atmospheric layer have been found, we can find the thickness of each layer as follows:
̅ ( )
Fig. 3 This figure shows the dwarf planet Pluto with an engineered atmosphere around it. The distention of 1660 kilometres will be explained ( ) shortly. ( )
The total height of the atmosphere will be the addition of ⁄ several discrete atmospheric layers. The thickness of the atmosphere will thus take the following form:
This will be done for each respective atmospheric layer. It (4) is very important to note, however, that the gravitational pull Assuming that one half the proportional pressure of the experienced upon each atmospheric layer is significantly Plutonian atmosphere corresponds to the atmospheric pressure different. Thus, the gravitational pull will need to be of the Earth’s atmosphere with respect to the atmospheric recalculated for every layer. Rather than integrating over the 4 entirety of the distention of the atmosphere, a simple IV. THE EFFECTS OF SPUTTERING ON A PLUTONIAN recalculation of the gravitational pull at the top of each ATMOSPHERE atmospheric layer will be accomplished for simplicity The primary issue with developing such a humongous purposes. atmosphere around the dwarf planet Pluto has to do with the Calculating the gravitational pull of Pluto with respect to sputtering effects generated by the Sun as well as other height above the surface is done as follows [8]: celestial bodies with significant magnetic fields. However, Pluto is roughly 39.2 times as far away from the sun as the
(5) Earth, indicating that the magnetic field of the Sun is 60,532
times weaker because magnetic field strength is inversely Where F1,2 is the force between two bodies of mass (M1 and proportional to the cubed distance from a specific frame of -11 3 2 M2), G is the gravitational constant (6.67384x10 m /kg s ), reference [10]. and r2 is the distance between the two bodies from each respective centre of mass. In the instance of a single celestial (7) 2 body, r is simply the radius of the planet itself plus the height above the surface. In addition, if M2 is of small enough mass, Using the planet Mars as a rough guide of atmospheric it can be omitted, and an approximation of the force due to sputtering, we can determine how long it would take to sputter gravity of Pluto can be found using the equation: away an engineered atmosphere from Pluto. During the epoch when Mars had a significant atmosphere, it is assumed that
(6) Mars’ atmosphere was roughly equivalent to 1 bar of pressure,
or very nearly the surface pressure of the Earth [11]. Despite this, once the dynamo of Mars dissipated, it took a mere 10
( ⁄ ) million years to dissipate the atmosphere from Mars [12]. Using the atmospheric mass equation, the rate of atmospheric
[ ] [ ] sputtering can be derived [4].
(8) ⁄
As can be seen, this is significantly different from the Where a is the radius of the celestial body, Ps is the surface gravitational pull at the surface of Pluto, 30.89% less to be pressure of the atmosphere, and g is the gravitational pull of more precise. This will significantly increase the overall size the celestial body at the surface. As such, the atmospheric of Pluto’s atmosphere. The table below shows the overall mass of Pluto, and that of a proto-Mars for approximation thickness of Pluto’s atmosphere: purposes is
Layer Thickness (m) Gravitational Pull (m/s2) ( ) H1 194,191.679 0.658 ⁄ H2 83,622.610 0.4547
H3 324,856.529 0.4075 H4 633,997.100 0.2706
H5 421,219.800 0.1477
H 1,657.890 km N/A tot ( ⁄ ) Table 2 This table is an organized form of the above equation iterated over each pressure interval using the Universal Law of Gravitation to recalculate the gravitational pull at each height. This atmosphere is absolutely gigantic, roughly 1.4 times With Mars’ atmosphere having dissipated down to a mere the actual radius of Pluto itself. However, even with this very 2.3432x1016 kg mass over the course of 10 million years, this large atmosphere, there is nothing preventing it from being means that Mars’ atmospheric loss rate was approximately sustainable, as will be illustrated. In addition, the current estimates for the upper limits of the atmosphere that Pluto already has indicate that it is well over 1200 kilometres above the Plutonian surface [9].
Based upon this rate alone, it would take roughly 3.447 million years for the engineered Plutonian atmosphere to 5 dissipate. However, as gravitational pull decreases, the effects This is a difference of 244 Kelvin, inarguably a humongous of sputtering are amplified. Also, as distance from the Sun required temperature increase, but it isn’t as difficult as some increases, sputtering effects are decreased due to a decrease in might expect. Using the mean temperature equation solar magnetic field strength. As such, the gravitational pull developed by Dr. Robert Zubrin and Dr. Chris McKay, the at the top of the hypothetical Plutonian atmosphere will be temperature change at the surface of Pluto with respect to an used for the most conservative estimate of dissipation rate. introduced atmosphere can be approximated [3]. Since the dissipation rate is a three-dimensional effect, the effect of sputtering will be cubed. (10)
Where S is the average solar output as a function of the ( ) (9) Sun’s age (we will assume it is always 1), and P is the atmospheric pressure of the planet in bars at the surface. I have further altered this equation to include the difference in
⁄ atmospheric thickness as a means of absorbing more solar ( ) energy, as I did in a previous paper [5]. ⁄
(11) 3.147 m/s2 is the gravitational pull at the top of Mars’ theorized atmospheric sputtering layer. But taking into Where H is the ratio of Pluto’s atmospheric thickness to the consideration Pluto’s distance from the Sun in astronomical atmospheric thickness of Earth. For instance, if Earth’s units as opposed to Mars’ distance from the Sun, the magnetic atmospheric thickness is 100 kilometres, and Pluto’s effect, as shown in equation (7), is drastically decreased. This atmospheric thickness is 300 kilometres, then the ratio would reduces the sputtering effect by a factor of be 3. As the thickness of an engineered Plutonian atmosphere
has been previously determined, the mean surface temperature
of Pluto would increase to ( )
This reduces the overall rate of sputtering by 26.1%. Though, it must be noted that this is quite a conservative estimate of the sputtering effect. The lowest gravitational pull of Pluto was used, as well as the three-dimensional rate of This still makes the required temperature increase 280 – sputtering [11]. Nevertheless, this means that such an 151.854 = 128.145 Kelvin. This difference can be overcome atmosphere on Pluto would face depletion over the course of using super greenhouse gases. 12.61 million years. This is similar to the dissipation rate that could be expected on an engineered Martian atmosphere, VI. HEATING UP PLUTO WITH GREENHOUSE GASES which is acceptable, though a means to avoid this sputtering The greenhouse effect on planets is still only scarcely will be discussed shortly. understood at this point in human history. Though, some
valuable information can be gleaned from the body of knowledge that has been developed thus far. From examples such as Venus, we can see that a runaway greenhouse effect on entire planets is not an uncommon occurrence, for it has happened once in our own solar system. If we look at the giant moon, Titan, we can see how having an atmosphere at all acts as a blanket upon the surface of a celestial body, heating it significantly above the solar equilibrium temperature. Then beyond this, we can see how a rarefied atmosphere such as that found on the moon can cause huge temperature swings. Even further, we have Mars, with such a tenuous atmosphere that a human being would instantly embolize without a pressure suit at its surface. The Fig 4 This figure shows a graphical (and exaggerated) representation of the atmosphere of Pluto will be engineered in such a way as to Sun’s sputtering effect on a familiar celestial body, Mars. This effect is what minimize distention above the surface, thus minimizing led to Mars’ atmosphere to being siphoned off over the course of several possible sputtering effects, while simultaneously providing million years. sufficient surface pressures to adequately sustain life. V. FINDING A MEANS TO INCREASE TEMPERATURE As it is, we are distinctly aware of the necessity of having a thick atmosphere that contains healthy amounts of heat- The mean surface temperature of Pluto is approximately 36 trapping molecules, such as water vapour, CO , methane, and Kelvin, yet the desired surface temperature is 280 Kelvin. 2 6 other gases. To figure out exactly how much greenhouse gas volumetric measurement because the density of any proposed would need to be produced on Pluto, we must refer to the atmosphere decreases rapidly with altitude. This would mean Earth’s atmosphere, and how it has evolved over the past 110 that the volumetric measurement of atmosphere would yield years due to human-induced global warming. The chart below much larger atmospheric numbers than a mass measurement. shows the increase in CO2 in the atmosphere of Earth in parts This is thus more conservative. However, it was merely done per million over the past 50 years, just to give an idea of this. as an engineering exercise and will not be reproduced in this The up-and-down pattern in the chart is due to the seasons; design. there is a greater land mass in the northern hemisphere of As such, having already calculated the atmospheric mass of 18 Earth as opposed to the Southern. As a result, the change in a ½ bar Plutonian atmosphere as 1.3547x10 kg, we can seasons sees a change in the total number of carbon-absorbing compare this to the overall mass of the Earth’s atmosphere. plants in bloom. However, the chart still shows a very clear Earth’s atmosphere is roughly 5.27x1018 kg [4, 15]. This trend upwards in CO2 levels [13]. means that the proposed atmosphere of Pluto is only 25.71% as massive as that of the Earth. This then means that only 12 8.483x10 kg of CO2 is required for the same ppm increase on Pluto, and thus the same temperature change. It must be noted that such a calculation is still a very inexact science at the current level of understanding of atmospheric evolution. It is not yet known if temperature increases are purely based upon ppm compositions of different elements, or if it has to do with a variety of other factors, such as atmospheric thickness, surface area of the proposed celestial body, etc. We will operate under this assumption, however, for this particular engineering design. Nevertheless, producing this much CO2 is a Herculean effort. Let’s consider a standard 600 MW coal power plant
Fig 5 This chart shows the increase in CO2 levels on Earth from 1960 to operating at full capacity 24/7. The amount of CO2 produced present day. per kilowatt hour (kWh) is as follows: Over the past 110 years, the global increase in temperature has been approximately 1 degree Celsius. During that time, Type of Coal CO2 Produced (lbs/kWh) Bituminous Coal 2.08 we need to determine how much CO2 humans have added to Sub Bituminous Coal 2.16 the atmosphere. The chart below shows the yearly CO2 production by humans during this time interval. Lignite Coal 2.18 Average 2.14
Table 3 This table shows the amounts of CO2 produced based upon the type of coal used [16].
With an average of 2.14 lbs. of CO2 produced per kWh, a single 600 MW power plant would produce
Fig 6 This chart shows the total production of CO2 from 1900 to present day in teragrams [14]. Over the course of the past 110 years, approximately 30,000 ⁄ teragrams of CO2 has been emitted into the atmosphere. This equates to 3.0 x 1013 kg. Thus As a conservative estimate, the maximum atmospheric pressure will be used for determining ppm composition of Pluto’s atmosphere. This is important because the current mass of the Plutonian atmosphere, which has a pressure of
only 0.3 Pascals at the surface, is only roughly 8x1012 kg. A different method will be used in this engineering design This would mean it would take 1 5 MW power plant 1 year to compared to my previous paper [5]. Rather than using heat up the Plutonian atmosphere by 1 degree Celsius. Since atmospheric volume to determine the total amount of CO 2 we do not know whether this is the case or not, and the required, atmospheric mass will be used to determine the atmospheric pressure would increase exponentially with the amount of CO required. This is much more accurate than a 2 number of power plants producing gases in addition to the 7 melting of surface ices, the most conservative means of 10,000 years. If the timescale is increased to 1,000 years, the determining greenhouse warming of Pluto is to assume its number of power plants required decreases to 54.408 or maximum desired surface pressure at the beginning. approximately 55. This atmospheric production would In addition, these power plants are not optimized to produce constitute only approximately 0.021% of the overall the maximum amount of CO2, so it is likely that tens to atmospheric mass, and thus would not significantly change the hundreds of times the amount of CO2 could potentially be specific gas constant, thus leaving the distention of the produced from the same amount of coal if such a thing were atmosphere and all other figures derived from it unchanged. desired. In addition to using SF6, such greenhouse gas-producing Under these assumptions, it would take 1,659 600 MW power plants would be optimized to produce said greenhouse power plants to increase the surface temperature of Pluto by gases, likely increasing the amount produced per MWH by a one degree Celsius in one year. However, a temperature rise factor of 100. With this taken into consideration, the total of 128.145 Kelvin is required, which means that it would take number of power plants is reduced to 0.54408, or one 330 212,606 power plants to produce such a temperature change in MWH power plant. one year. Though, this is predicated under the assumption that But what about atmospheric loss due to sputtering? the same amount of solar energy is received by Pluto as that of Determining the amount of atmosphere lost per year due to the Earth, which is not the case. The amount of solar energy sputtering is as follows: that Pluto receives with respect to Earth is
(12)
( )
Where I is the solar energy intensity, and d is the distance in astronomical units from the Sun. This means that the Earth A single 600 MW power plant produces 162.1 x (efficiency receives 1542 times the solar energy of Pluto, which thus factor increase=100) = 16,210 kg of atmospheric gases per means it would require 327,766,265 power plants to achieve second. This means that at least 0.5683 power plants would the required temperature change in one year. This number is be required simply to overcome the sputtering effects caused astronomical, but as we will find, it is astronomically reduced by the Sun at this distance. Thus, the grand total number of by yet more factors. power plants required to produce a significant atmosphere on First of all, CO does not need to be the greenhouse gas of the surface of Pluto is slightly more than one for a 1,000-year 2 period (1.112). This makes for a total of 670 megawatts of choice. If, instead, we choose to use SF6 (sulphur hexafluoride) for greenhouse warming of Pluto, then the energy production on Pluto. However, taking into consideration the maximum gravitational pull of Pluto and the situation changes. SF6 is 20,000 times as efficient at trapping solar energy when compared to CO [12]. This means that it initial rarefied atmosphere, it would take no more than one 30 2 MW power plant to begin the terraforming effort at first. would require 20,000 times less SF6 for the same temperature change. Thus, the mass required for the same temperature These figures are not so ridiculous as to be entirely increase becomes unfathomable. Human civilization has only been in existence in an organized fashion for roughly 10,000 years. Technological innovation has only in the past 200 years
reached true prominence. In the last 200 years alone, humanity went from barely having invented the steam locomotive to sending probes billions of miles into space. This reduces the number of power plants required to 16,388. With the exponential growth in technology and innovation, But the efficiency of SF6’s heat trapping is not based upon a attaining a 690 megawatt energy production capacity on a far- per mass basis, but a per molecule basis. This means that flung world may seem inconsequential 1,000 years from now.
Indeed, on Earth, it already is, with global energy production ⁄ topping 14 terawatts per year [17].
⁄ VII. OTHER CRUCIAL ATMOSPHERIC EFFECTS
An important factor to take into consideration when
engineering an atmosphere on Pluto is the large amount of
frozen nitrogen on the surface of the planetoid. Based upon Increasing the number of power plants required to 54,408. the vapour pressure of N that constitutes Pluto’s tenuous However, the temperature increase does not need to be 2 atmosphere, it can be assumed that there is anywhere between accomplished in a single year. Indeed, such an engineering several million, to several tens of millions of square endeavour would be planning for the long term. Thus, the kilometres of frozen N on the surface [18]. N turns into a timescale could reasonably be increased to 100, 1,000, or even 2 2 8 gas at approximately 77.355 Kelvin [19], which means that a ( ) temperature increase of only roughly 41.355 Kelvin would be necessary to cause the entire bulk of surface N2 to boil off.
Of course, this is assuming an equal distribution of frozen N2 over the entirety of the Plutonian surface. Current models predict that the amount of frozen N2 on the surface of Pluto is not equally distributed, but patchy. This is evidenced through the unequal albedo of Pluto’s surface, as shown in the figure below. Even so, this estimation for N2 abundance is highly likely to be extremely conservative, with Pluto’s surface possibly covered in patchy layers of frozen N2 several kilometres thick [18].
’ Fig 7 This figure shows an liquid nitrogen as it appears on Earth. While much of the liquid boils off into gaseous nitrogen on our home world, on Pluto, N2 would not reach boiling temperature for quite some time. However, once it did, a massive atmosphere would likely result.
The question then becomes, how much of this N2 is there, and how much of it would be required to cause a runaway atmospheric genesis? If this occurred, which is highly likely based upon the temperature increase, producing an Fig 8 This figure shows the clearest images of Pluto’s surface to date, as atmosphere on Pluto would no longer be an issue; the only viewed through the Hubble Space Telescope. remaining issue would be increasing the temperature of said One way or another, an average thickness of 0.07488 km3 is atmosphere. This same runaway atmospheric genesis is more than reasonable, and even expected when more accurate believed to be fundamentally possible on Mars as well, only measurements of Pluto’s surface are received by the New with different molecules constituting the Martian atmosphere Horizons space probe, which will reach Pluto in mid-2015 [3]. 3 [20]. This frozen nitrogen layer has very important Frozen N2 has a mass of 1.027 g/cm . The mass of ramifications on the ease of terraforming Pluto. If this atmosphere that needs to be produced is nitrogen layer is indeed present, it would mean that the surface of Pluto would only need to be heated by slightly
more than 40 Kelvin before a runaway atmospheric thickening would occur. However, this would also significantly change the albedo of Pluto’s surface, as frozen nitrogen has different reflective characteristics when compared to clean, frozen With these numbers, we can determine the square area of water. Clean, frozen water has an albedo of approximately solid nitrogen required in order to produce a significant 0.8 [21]. With this increase in albedo, the equilibrium atmosphere. temperature of Pluto would decrease from its current 36 to 44 Kelvin down to
( ) ( ) ( )
√ √ ( ) [ ]
With this, we can then find the required average thickness of a nitrogen ice layer on the surface of Pluto. This is done as follows: The difficulty that arises from this decrease in temperature is maintaining a subsequent increase in temperature of the surface that outpaces the boiling off of frozen nitrogen and 9 thus increase in albedo of the surface of Pluto. This should be This is evidenced through the giant moon, Titan, where easily overcome, as it takes several hundreds to thousands of surface winds at peak intensity reach no higher than 5 miles years for a celestial body to reach a new equilibrium per hour [7]. This is compared to Earth, where average temperature with a significant change in albedo, but surface winds are approximately 20 miles per hour. The giant nevertheless, it must be addressed in some way here. This moon, Titan, orbits at a distance approximately 10 times decrease in surface temperature of Pluto would then change farther away from the Sun than the Earth. This means that a the mean surface temperature based upon Zubrin and rocky Plutonian surface would not face extreme erosion due to McKay’s equation to roughly 145.579 Kelvin. winds, and thus any solid rock formations would remain for This is still well beyond the boiling temperature of N2, and an exceptionally long period. thus should not pose any noteworthy issues. Though, it is possible that during the early stages of Pluto terraforming, N2 ice could boil into gas, and quickly form back into liquid or ice. Until a certain critical point of boiling rate is reached, Pluto will revert back to a natural state of equilibrium with frozen N2. This is a negative feedback system, but it can be broken with a significant engineering effort. Such an effect is also theorized to be expected in a terraforming effort on Mars [3]. The figure below shows two separate equilibrium temperatures for Mars’ surface.
Fig 10 This figure shows the giant moon, Titan, as viewed in false colour. This image provides a view of the surface of Titan while at the same time clearly showing the massive size of the moon’s atmosphere. But a water world Pluto does not pose significant problems, and in fact, makes terraforming somewhat easier. Water has a Fig 9 This graph shows an example of two different equilibrium temperatures low albedo compared to other possible surface compounds, on Mars. Such a situation could also be experienced on Pluto, once sufficient such as silicate sand. This means that Pluto would absorb frozen nitrogen is sublimated to produce a massive and warmed atmosphere. more solar energy, and thus would require less constant It must be understood that Pluto will never have a surface heating from greenhouse gas production. So, while the truly similar to that of the Earth in that, because of Pluto’s equilibrium of Pluto would be difficult to move past the composition due to its distance from the Sun, its surface will frozen and liquid nitrogen stages, once done, a slow evolution become covered in liquid water. Pluto is comprised towards a liquid water stage could be a much easier transition. approximately of equal parts water ice and silicate rock [18], but its surface in particular has a large amount of frozen water mixed with frozen nitrogen and methane. Indeed, warming Pluto would likely turn it more into a mini-water world, rather than a super-low-gravity planet. It is possible that small patches of solid rock land formations would be present, but below the rock-ice mantle of Pluto lies what is believed to be a liquid ocean. Any solid landforms would be nothing more than mere floating islands. Nevertheless, due to the lack of tectonic plate movement on Pluto because of its very small size and low internal heat, such landforms would likely not risk devolution below the liquid layer to any large degree. This is also due to the low amount of solar energy that Pluto receives. With such a low solar Fig 11 This figure shows an artist’s concept of a cold water world. As can be energy, the wind currents in an engineered Plutonian seen clearly, this planet has very large polar ice caps and is shrouded in thick cloud layers. atmosphere would be very subtle, perhaps almost non-existent. 10 One of the biggest barriers to having a water world is that there is little to no surface for photosynthetic plants to take root. Though, thankfully, water can make up for a large portion of the oxygen issues due to its molecular structure. Water naturally breaks down into its constituent elements over long periods of time, albeit in rather small amounts [4]. But, over several thousands to several millions of years, this can produce enough atmospheric oxygen to render a water world’s atmosphere breathable, perhaps even more so than a planet covered in vegetation.
VIII. LUMINOSITY AND PLANT LIFE ON PH So, we have discussed how to actually make Pluto warm enough for humans to comfortably survive at the surface without pressure suits or body-heating apparatuses. But how habitable is it to the flora and fauna upon which human society so keenly relies to thrive? At these distances, it truly does start to become very difficult for plant life to thrive. Fig 12 This figure shows a scanning-electron image of a water bear. Water Unlike PH, a previously designed hypothetical planet over 2 bears (also known as tardigrades) are known to be able to survive in billion kilometres distant from the Sun where light levels were environments with literally no atmosphere (i.e. outer space). They can live still significant enough for some of the most shade-tolerant without water for decades, and can be brought back to life if frozen. plants to thrive, on Pluto, the issue becomes entirely different. Pluto receives only 0.0649% the sunlight that the Earth receives (0.883 watts/m2), and only 16.73% the sunlight that 2 PH receives (5.281 w/m ) [5]. In addition to this, while it may be possible to genetically engineer plants to live in such low light levels, Pluto will likely have no solid surface, as previously stated. This means that any flora would need to be birthed deep beneath the Plutonian surface, in the depths of an ocean. This surface ocean could be anywhere from several hundred meters to several hundred kilometres thick. At the bottom of such an ocean, even in the shallowest locations, solar luminosity would be practically zero. Nonetheless, even in these extreme circumstances, there are workarounds. First of all, assuming Plutonian flora would be genetically engineered to endure the low light levels, such photosynthetic flora could float at the surface of a Plutonian ocean, much in the way that seaweed floats through the ocean on Earth. This would mean that any sunlight that Pluto does receive could be absorbed by these floating plants with minimal oceanic diffraction. But beyond even this, intense study of newly discovered organisms and ecosystems on Earth Fig 13 This figure shows a bacterium that has evolved to consume toxic waste. that do not require photosynthesis even at their lowest tropic But once more, beyond even this, there may not be a levels is being carried out. In the deepest depths of the genuine need for flora to grow on Pluto at all. If sufficient Earth’s oceans where practically no light can reach, atmospheric oxygen can be produced from the hydrosphere ecosystems have been found that rely exclusively on bacteria alone, and the ocean covering Pluto produces a significantly that consume nutrients produced by tectonic activity on the large amount of warmth through its increased albedo, then the ocean floor, nutrients ejected by hydrothermal vents [22]. only issues a human civilization would need to endure are (1) These organisms are aptly named extremophiles, for they procuring food, (2) procuring desalinated water, and (3) thrive in what humans consider extreme environments. developing an efficient and feasible method of producing floating colonies and energy production facilities. Given the long timescales of such an engineering endeavour, these issues could be tackled in perpetuity as they arise. But what about light levels for humans? The question then becomes, are these light levels on Pluto sufficient for humans to conduct vital day-to-day activities? Let’s put this into perspective. We will use a typical 60-watt light bulb to give 11 us a better understanding of light levels. A 60-watt light bulb The light level on Titan is approximately 15.4 times that produces 840 lumens of brightness through a soft-white- which reaches the surface of Pluto. On the surface of Pluto, painted glass sheath, whereas a typical candle produces 12 the light level is equivalent to a very bright street light, or on lumens of light. A lumen is a measure of luminous flux. On a average about 250 times as bright as the full moon [23]. typical day at the equator of Earth, the sun provides 93 lumens per watt. From the 60-watt light bulb, we get
This means that the Sun provides
Or, put another way, the 60-watt light bulb provides 15.05% the luminosity of the Sun. To put this into clearer perspective, the luminous energy per watt on the surface of the giant moon Titan is only 1% that of the Earth. The figure below shows the ambient light level of Titan.
Fig. 15 This picture is a good comparison for the brightness that one may experience on the surface of Pluto at its current distance from the Sun. While much dimmer than daytime, these light levels are more than sufficient to conduct activities that require high levels of visual acuity.
Fig. 16 This picture is a good representation of the light levels that may be experienced on a Pluto with an engineered atmosphere. It is unlikely that wooded plants or large, rocky landmasses would be commonplace on Pluto, but the light levels are quite accurate. Assuming a human being with normal vision can write in the light of the full moon, these light levels are more than adequate for day-to-day activities. Though it is likely that, for instance, driving a car would require one’s headlights to be on Fig. 14 This picture shows the typical brightness at the surface of the moon constantly, no matter what time of day. Titan. While this light level is still some 15 times greater than what would be Through all of this, we can determine that the light levels experienced on the surface of Pluto, it nevertheless is quite bright. on Pluto would be in a range that would start to degrade 12 human survivability, unlike PH as shown in the previous paper its current mass. But, there are other methods that can be in this series [5]. Even so, this analysis shows that human employed in order to minimize and even entirely eliminate the survivability on Pluto would not be impossible, and in fact, in sputtering effect on Pluto. many aspects, it would be easier to proliferate on Pluto as Let us take the hypothetical planet, PH, which was designed opposed to PH or even Mars. In order to really push the in the previous paper in this series. PH has a significant envelope of human ingenuity, we require daring and magnetic field, one of which was engineered primarily to imagination, something that allows you to go beyond the folds prevent the effects of atmospheric sputtering. This of normality, to think outside the box. Impossibility is a atmosphere can also be used to protect a terraformed Pluto in concept based in limitations that people put upon themselves. the same way. This would require engineering not only on a Nothing is impossible. All that one need do is to first believe planetary scale, but on an intrastellar scale. That is to say, in possibility. This endeavour is more than within the Pluto could be moved into an orbit around PH that would purview of our civilization; even now, Pluto could be allow for the dwarf planet to be protected by the immense terraformed, though it would likely cost several quadrillion magnetic field that PH generates. Not only would Pluto be USD. protected by PH’s magnetic field from sputtering, but less of an effort would be required to heat the surface of Pluto due to IX. ANOTHER MEANS TO PREVENT SPUTTERING? its closer proximity to the Sun. Once more, the prospect of As described earlier, sputtering is a serious problem for photosynthetic plants proliferating on a Plutonian surface re- Pluto, even at its immense distance from the Sun. Taking into emerges. consideration all the factors mentioned in this paper thus far, it would take approximately 12.61 million years for an engineered Plutonian atmosphere to be stripped away back to
Fig. 17 This figure shows what a typical day may look like on the surface of PH, with Pluto looming high in the sky. The Sun is far smaller than Pluto in the sky due to its extreme distance from PH. Consequently, the sky is far darker than a typical day on Earth. It is important to note that if Pluto is put into too close of an manifests in the form of large, highly lethal radiation belts that orbit around PH, the dwarf planet could face a variety of surround the planet. In the case of the Earth, the Van Allen potential problems. First of all, every celestial body with a radiation belts are a key example [24]. significant magnetic field which deflects large amounts of solar wind/radiation, requires that this deflected material go somewhere other than the surface of the body. This usually 13 would require much larger amounts of energy to place Pluto in a shallow orbit around PH, and thus is preferable to give Pluto a larger orbit. These tidal forces and their effects on Pluto and PH will be elaborated upon later. While placing Pluto into a more distant orbit from PH is preferable, how far is this distance? Clearly, Pluto must be placed somewhere in the vicinity of PH’s magnetic field in order to attain any level of protection from solar wind. The extent of PH’s magnetic field is 392,993.4 kilometres [5]. There are a few more issues with which must be contended before the decision can be made. The first is of the magnetic Fig. 18 This figure is a representation of the Van Allen radiation belts around field lines. Pluto cannot be placed in an orbit that will for any the Earth. Though not to scale, it illustrates the general shape of the belts extended period of time put it in the direct path of any of PH’s quite well. They surround the Earth; this is a cut-out view. magnetic field lines, for if Pluto is in contact with PH’s magnetic field lines for any significant amount of time, this These radiation belts for smaller, Earth-sized planets with can create an induced magnetic field effect on Pluto, which magnetic fields of moderate strength typically do not extend thus can amplify the atmospheric sputtering effect rather than beyond 10 planetary radii above the planet’s surface. In the reduce it [25]. The giant moons Callisto and Io of Jupiter can case of PH, this would be 100,000 kilometres above the surface. These radiation belts pose a number of problems for be used as a clear example of the effects of this. Both moons have an induced magnetic field caused by their interactions Pluto. First of all, a radiation belt would make the surface of a with the magnetic field lines of Jupiter as well as potential non-terraformed Pluto more or less uninhabitable for humans liquid oceans that at least Callisto may harbor below its without great measures put in place in order to protect against cratered surface. Despite Io producing several thousands of the harmful radiation. Any extended stay in such a location would be very difficult. Second, placing Pluto in such a tons of material per second due to its high degree of radiation belt could actually amplify the atmospheric leeching volcanism, a mechanism which should produce a significant atmosphere of some type, Io has almost no atmosphere effects caused by solar wind. This is because the engineered whatsoever. This is because Jupiter’s magnetic field leeches it atmosphere of Pluto would react with the excited material in away at a faster rate than Io’s volcanism can produce it. Even the radiation belts, and would rapidly dissipate. What would Ganymede, the only moon in the solar system known to have normally take Pluto 12.61 million years to have its atmosphere dissipate could be reduced to as little as 10,000 years its own magnetic field, is prevented from having a significant conservatively. atmosphere for the same reasons [25].
Again, even with a significant atmosphere on Pluto, having Pluto anywhere near such a radiation belt would drastically increase the probability of getting cancer at the surface. This is because Pluto does not have a magnetosphere itself, and thus cannot deflect the radiation as efficiently as PH. Additionally, the proposed atmosphere on Pluto would only be half as dense at the surface as compared to that of Earth, which indicates itself a vastly reduced capacity to protect against celestial radiation. A clear example of this is the planet Mars. On Mars, the atmosphere is a mere 6 millibars of pressure (1/150th of Earth). In such an environment, it takes roughly 2 years to acquire 60 REM of radiation, an amount that would take an airline pilot on Earth an entire lifetime to acquire [3]. Another important issue with which to contend is that of tidal forces. Though Pluto is a tiny celestial body when compared to PH, it nevertheless can exert an impressive gravitational force upon PH. The closer Pluto is to PH, the stronger the force, based upon Newton’s Law of Universal Gravitation. While 100,000 kilometres from the surface Fig. 19 This picture shows the surface of the giant moon, Io. As can clearly would likely produce similar effects on P to that of what the be seen, Io is a highly volcanic world. Despite this, Io has almost no H atmosphere. This is because the moon is bathed in high intensity radiation of Moon causes on Earth’s surface, it remains an important issue Jupiter, and is constantly having its atmosphere stripped away by the gas to be considered in such an engineering design. Moreover, the giant’s magnetic field. closer Pluto is to PH, the faster it needs to orbit in order to maintain its altitude. This is due to the conservation of angular momentum. In such an engineering situation, it 14 fact, Titan’s atmosphere has 1.45 times the surface pressure of Earth’s atmosphere. Key to this seems to be the absence of solar wind, or any magnetic field effects at all from either Saturn or the Sun. A similar method can be employed for Pluto. For these reasons, an orbital radius of 390,000 kilometres will be chosen for this design. This orbital distance does not cause excessive tidal issues, prevents interference from any possible radiation belts, and minimizes the risk of intercepting the magnetic field lines of PH for any extended period of time. The magnetic field of PH at this distance is described by
(13)
( )
Where BE is the magnetic field strength, BO is the magnetic field at a specific frame of reference (in this case, the surface of PH), d2 is the orbital radius of Pluto, and d1 is the radius of PH. Thus, the magnetic field strength is
Fig. 20 This figure shows the magnetosphere of Ganymede as affected by ( ) Jupiter. While Io and Callisto do not have magnetospheres of their own like Ganymede, the induced magnetic field effects are more or less the same. This would strip away significant atmospheres very rapidly. At this distance, the Sun’s magnetic field intensity is As one moves farther away from PH, the magnetic field 0.00121 nT. This puts the sum of the overall intensity at lines become much more dispersed, so much so in fact that an 0.00002 nT. With such a weak magnetic field effect, this entire celestial body could orbit comfortably within the space would reduce atmospheric sputtering so much that it would between two sets of magnetic field lines. A distance take a Plutonian atmosphere roughly 4.1 times as long to sufficiently far from PH will thus be chosen that is more than dissipate, putting the longevity of the Plutonian atmosphere at 100,000 kilometres distant, but less than 394,000 kilometres. approximately 51.7 million years. This can be reduced even The final issue to take into consideration is that of the further with more exact orbital placement with relation to PH’s magnetopause of PH, the point where the solar wind’s strength magnetopause. Additionally, this is not even taking into matches the strength of PH’s own magnetic field. This was consideration Pluto’s natural rate of atmospheric generation, already shown to be approximately 394,000 kilometres distant, which is on the order of several thousands of kilograms of however, this is an important concept to understand. The material per second [9]. giant moon, Titan, orbits Saturn at a distance that places it very close to the magnetopause of Saturn, approximately 1,200,000 kilometres. Ironically, Titan is the only known moon in the solar system to have a significant atmosphere. In 15
Fig. 21 This figure shows the relative orbit in which Pluto would be placed with respect to PH and its magnetic field. The orbital distance of 390,000 kilometres would put Pluto very close to the magnetopause (if not within it), which would then cause Pluto to experience similar sputtering effects to that of the giant moon, Titan. This figure is not to scale. A very important thing to understand is that scientists,
prior to the Voyager missions which visited Saturn, originally ( ⁄ ) believed that a body with a surface gravity as low as that of √
Titan could not sustain an atmosphere of any significant mass. In truth, our science has only just begun to scratch the surface of the possibilities. Without the effects of a magnetosphere on a celestial body, the potential for even a naturally occurring atmosphere on such a small body as Pluto becomes a real one. This means that, it would take Pluto 23.73 days to make Placing Pluto as close as possible to the magnetopause of PH one complete orbit around PH. Assuming Pluto has no could sustain an atmosphere on the dwarf planet in perpetuity, rotational velocity itself, this would add to the difficulty of with no need for extensive human modification whatsoever. producing photosynthetic plants. To understand the magnitude of this problem, it is necessary to determine the X. OTHER IMPORTANT FACTORS mechanism of tidal locking on Pluto with respect to PH. The Placing Pluto into such an orbit would come with some length of time it would take Pluto to tidally lock with PH with consequences. First of all, at a distance of 390,000 kilometres respect to distance and starting rotational velocity is from PH’s surface, the orbital velocity of Pluto is described by approximated through the following equation [26]:
√ (14) (15)
Where is the initial spin rate in radians per second, a is Where G is the gravitational constant, m1 is the mass of PH, the semi-major axis of the satellite (Pluto), I is the moment of m2 is the mass of Pluto, and r is the radius of the orbit itself plus the radius of the celestial bodies. Thus, assuming a inertia of the satellite, Q is the dissipation function (which for perfectly circular orbit with no eccentricity, the velocity works simplicity purposes is approximated to be roughly 100), G is out to be the gravitational constant, mP is the mass of the planet, ms is the mass of the satellite, k2 is the tidal love number of the satellite, and R is the mean radius of the satellite. These 16 figures or their approximations are straightforward with the this case, to maintain a rotational velocity, large celestial exception of the moment of inertia and the tidal love number, bodies could be used to speed up the orbit of Pluto. so let’s delve into these two concepts before we find the time Additionally, with such a far-reaching engineering project, to tidal locking. The equation to find the moment of inertia of there would likely be a plethora of technologies available at a satellite like Pluto is approximated by the disposal of humanity 10 million years in the future to perpetuate a sufficient rotational velocity for Pluto, such as,
(16) perhaps inter-dimensional wormholes used for teleportation and propulsion purposes. The possibilities are endless. Such This makes the moment of inertia of Pluto 7.3176x1033 kg engineering feats have already been discussed with regards to m2. The tidal love number is the tricky one to determine for culling entire asteroids into orbits around Earth for mining Pluto, however. The tidal love number is basically a measure purposes, so this is not an unimaginable task [27]. of the flexibility of a celestial body, and thus with this you can get a determination of how much the gravity acting upon the XI. A FEW MORE INTERESTING FACTS body will affect its spin rate. The equation for the love As it appears, the development of a habitable Pluto is number of Pluto is approximated as [26] highly possible, but there are always more variables to take into consideration due to humanity’s ever-limited understanding of the cosmos. One interesting concept to (17)
understand is that of barycenters. In Pluto’s current orbit, it has a giant moon relative to its own size, a moon that is over Where is the rigidity of the satellite (3x1010 N/m2 for 10% the mass of Pluto itself: Charon. This moon-dwarf rocky objects and 4x109 N/m2 for icy objects), is the density planet pair is so close in mass and the celestials bodies far of the satellite (2.03 g/cm3 for Pluto), R remains as the radius enough away from one another that the barycenter of the of the satellite, and g remains as the gravitational pull of the system lies outside the surfaces of both Pluto and Charon. satellite at its surface. For Pluto, since it is theorized to be comprised of a mixture of equal parts rocky and icy material [9], a rigidity of 1.7x1010 N/m2 will be used. This gives a tidal love number of
[ ⁄ ] ( ) ⁄ [ ] [ ] [ ⁄ ]
This falls in line with other celestial bodies close to Pluto’s Fig. 22 This figure shows the barycenter of the Pluto-Charon system. As can size. For example, the moon has a tidal love number of be seen, the barycenter lies beyond the radius of Pluto. 0.0266. The larger the celestial body, the bigger the love It brings up an interesting idea: where would the barycenter number. Jupiter-sized planets have love numbers in the tens of a Pluto-PH system be? As it turns out, this is exceptionally to hundreds of thousands. Let’s assume that Pluto has an easy to calculate. Calculating the barycenter of a planetary initial spin rate that would give it roughly a 24-hour day. This system involves taking the mass of the less massive of the two -5 spin rate in radians per second is 7.2722x10 radians/second. bodies in the system, and dividing by the overall mass of the Thus, the length of time it would take Pluto to tidally lock to entire system. You multiply this number by the overall orbital PH is 11,320,896 years. This is a relatively short period of radius of the system, and you get the system’s barycenter. time. But it also must be noted that this calculation is a rough This gives the distance away from the center of mass of the approximation. It has been known to be off by as much as a larger of the two bodies. The calculation is as follows: factor of 10. For instance, the time it would take for the Earth to tidally lock to the moon is believed by a consensus of (18) scientists to be roughly 2.1 billion years, but using this approximation, the answer comes out to roughly 20 billion years. As such, this tidal locking time could be anywhere from 110 million years to 1.1 million years. Under any of these scenarios, such a problem would make photosynthesis on the surface of Pluto a highly difficult task. Though, it still is not impossible. I’m going to push you as far as you can go. Nothing that In this case, the barycenter would be well within the radius you can perceive is impossible. There is a way to do it. In of PH itself, preventing the possibility of any egregious orbital 17 perturbations. One can do this calculation with any two (this produces a surface temperature that averages out to be bodies in the universe, assuming the masses of the two objects approximately 85 degrees Fahrenheit, as opposed to 59 are known. degrees Fahrenheit for Earth)? Strip away these limitations And finally, probably the most interesting artifact of and start thinking of grander possibilities. That is what creating a habitable atmosphere on Pluto is the terminal science truly is all about. velocity. Due to the far lower gravitational pull on Pluto, the 1,000 years ago, an airplane would have been thought of as terminal velocity has the potential to be much slower than on impossible; for that matter, the simple technology that is a Earth (122 miles per hour for a human being). A good pocket lighter would have been considered magic. During the example of this is Titan. On Titan, the terminal velocity is a 17th century, Giordano Bruno was burned at the stake for mere 12 miles per hour, slow enough to fall from the top of believing that there were worlds beyond Earth [29]. About a the Titanian atmosphere all the way to the moon’s surface and century later, Isaac Newton was a social pariah for many of safely touch down without a parachute! A similar effect the same reasons. Galileo Galilei was put on house arrest for would be experienced on Pluto, though, since Pluto has only explaining the motion of the planets around the Sun and other half the surface pressure of Earth, this factor slightly increases celestial bodies. All of these people pushed the boundaries of the terminal velocity. The overall terminal velocity of Pluto what was considered true or even possible. It is the would become roughly 16.4 miles per hour. Typically, a responsibility of the scientist, or all of us for that matter, to parachutist on Earth will touch down between five and 15 never settle for the currently understood, but continually push miles per hour. This means that, as with Titan, one would not back the curtains of ignorance. ever need a parachute to safely touch down on the surface of Nothing is impossible. The only impossibilities are those Pluto! created from human-perceived limitations. But, in order for anything to be accomplished, you must first believe. XII. CONCLUSION Now we have had two papers expanding upon the idea of ACKNOWLEDGMENTS artificial habitability zones around stars. So, what defines an 2LT Payton Pearson wishes to acknowledge 2LT William artificial habitability zone? In truth, it is the human desire to Giguere for helping in the initial review process of this paper, actually make a celestial body habitable—there is no real limit as well as providing ample support in the project. 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