The Universe in my pocket

The

Gloria Delgado Inglada 4 No. 4 Instituto de

Astronomía, UNAM, Mexico Formation of the Solar System

Our Solar System formed around 4600 million years ago. We know this from the study of meteorites and radioactivity.

It all began with a cloud of gas and dust. A nearby supernova explosion The Solar System is composed of the probably perturbed the calm cloud, Sun and of all the bodies travelling which then started to contract around it: , dwarf planets, , due to gravity, forming a flat, asteroids, comets, meteors … rotating disk with most of the Almost 25 objects in the Solar System material concentrated in the have sizes bigger than 1000 kilometers: center: the protosun. the Sun, the four gaseous planets and the four -like planets, five dwarf Later, gravity pulled the rest of planets, and around 12 moons and the material into clumps and trans-neptunian objects. rounded some of them, forming the

The other constituents (asteroids, and planets and dwarf planets. The dust particles) are much smaller. leftovers resulted in comets, asteroids, and meteoroids. 2 3

The Sun The Sun is a star. It lies at the center of the Solar System and contains 99.9% of its .

The Sun is an average-mass star. The biggest stars have one hundred times larger, while the Above: The Sun, seen through different smallest ones have have masses ff telescopes, each collecting light at di erent ten times smaller. wavelengths (colours). Observing various types of light allows astronomers to study All the heat and light that we various physical processes. receive from the Sun come from its For example, sunspots are dark in the visible nucleus where the fusion of (400 to 700 nm) whereas in the ultraviolet hydrogen is occurring. The they are bright. at the center of the Solar flares are bright in the extreme ultra- Sun is15 million degrees Celsius. violet (10 to 100 nm) and X-rays (1 to 10 nm). Right: An aurora. It is due The magnetic field of the Sun to collisions between causes a variety of phenomena charged particles from such as sun spots, flares, storms, the Sun with atoms in and the beautiful auroras occuring the Earth’s atmosphere. on Earth. 4 5

ff Balls representing the di erent planets of the Solar system. In each image the The planets relative sizes of the planets have been The first official definition of a respected. was given only in August, 2006 by From left to Mars the International Astronomical Union right and top to (IAU). With this definition bottom: `stopped’ being the ninth planet. Left: Earth, Venus, A planet is a body that: Mars, Mercury. 1) the Sun, Right: 2) has enough mass to be rounded by Jupiter, , its own gravity, and Uranus, , 3) has cleared its neighborhood of Earth, Venus, minor objects. Mars, Mercury. Objects that satisfy 1) and 2) but not 3) like Pluto or are called dwarf planets. Left: The Sun, Jupiter, Saturn, The Solar System contains eight Uranus, Neptune, Earth, Venus, planets: four earth-like planets Mars, Mercury. (Mercury, Venus, Earth and Mars) and four gaseous planets (Jupiter,

6 Saturn, Uranus, and Neptune). 7

Left: Ceres is the Minor bodies biggest asteroid in the Galaxy interactions Main - Asteroids are rocks that the and a . Sun. Their sizes range from one to 950 The image shows the kilometers. They are mostly found in a enigmatic bright ring between Mars and Jupiter, called spots on its surface. the main asteroid belt. Right: Philae - Comets are balls of and dust that was the first arise from the and from the instrument . Occasionally comets that landed on approach the Sun, which melts them. a comet, 67P/ One of the most famous comets is Churyumov- Gerasimenko. Halley’s Comet, which visits us every 75 years. Left: The - Meteoroids are rocks that travel meteorite `La through the solar system. If they enter Concepcion’. It weighs more Earth’s atmosphere they are called than 3 tons. It meteors, or shooting stars. If they is exhibited in survive to reach the surface of the the Institute of Earth, they are called meteorites. Astronomy, in - Moons are bodies that orbit planets Mexico City. or dwarf planets. 8 9 Left:

The Main TheZones Hubble in the tuning Solar fork System Asteroid The Main Asteroid Belt contains Belt, billions of asteroids. These bodies between formed at the begining of the Solar Mars and System and were trapped in this Jupiter. annular region by Jupiter’s gravity. Right: The Kuiper The Kuiper Belt contains hundreds Belt is of thousands of comets and other located bodies, such as Pluto. beyond the orbit The Oort Cloud is a cloud of small of bodies at the edge of the Solar Neptune. System. It is so far away from us

Representation on Left: and so big that Voyager 1 (a logarithmic scale The Oort spacecraft launched in 1977) will Cloud take hundreds of years to reach it contains and thousands of years to leave it. trillions of At the speed of the light icy bodies at the edge (300,000 kilometers per second), of the Solar it takes one year to travel from System. the Sun to the Oort Cloud.

10 11 Artists’s picture Galaxy interactionsshowing a view of GalaxyOther interactionsplanetary systems the surface of the Our Sun is only one of the hundreds planet Proxima b of thousands of millions of stars* discovered around that exist in the Milky Way, our the closest star galaxy. The Milky Way is just one of Proxima Centauri. the 1011 galaxies that exist in the Universe. Thus, how many planetary systems do you expect to exist in the whole Universe? This is a hard question because there are many different types of stars: some of them are very hot while others very cold. Some of them are isolated like our Sun while others are grouped into clusters. We can only imagine that many of The habitable zone is the region around a star where liquid water can exist on the the stars in the Universe may have surface of a planet (because the temperature planets around them. is neither too high nor too low). The green The first exoplanet was discovered belts in the image above show the habitable in 1988. By the end of 2016, zones in some recently discovered 3540 exoplanets were known! planetary systems. 12 * also written 1011 13

YES Quiz Solutions

NO

Pluto is a dwarf planet Andromeda is a of the solar system galaxy with many solar systems

Do these YES objects belong to the Solar

System? 67P/Churyumov- Gerasimenko is a comet in our solar system NO

Proxima Centauri YES is the closest star to our Sun 90482 Orcus is a Solutions on Trans-Neptunian overleaf object

The Universe in my pocket No. 4

This booklet was written in 2016 by Gloria Delgado Inglada from the Instituto de Astronomía, UNAM (Mexico) and revised by StanNr Kurtz 1 from the Instituto de Radioastronomía y Astrofísica, UNAM (Mexico).

The cover image is an artist’s representation of the Solar System with its star (the Sun), eight planets, and130 moons, comets, asteroids, rocks, and dust particles. Credit: NASA. The other images are mostly from NASA, ESA , and the Hubble archives.

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