Asteroids Near and Far

David J. Tholen Institute for Astronomy University of

Subaru 20th Anniversary 2019 November 22

Subaru and Near-Earth

● Wide, deep imaging one of Subaru's strengths ● One of my earliest uses of Subaru was to look for asteroids interior to the Earth's orbit ● Introduced the term “apohele” to refer to this type of object (to distinguish from Amor, Apollo, Aten near-Earth objects) ● The motivation...

Asteroid aphelia circa 2000

The Search for Apohele

● UHAS81 discovered 2004 Dec 13 with Subaru ● Later designated 2004 XZ130 ● At the time of discovery, had the smallest semimajor axis of any known

Orbit of 2004 XZ130

Asteroid aphelia circa 2019

List of Known Apohele

Object Aphelion Distance (AU) 2019 AQ3 0.77 2019 LF6 0.79 (418265) 2008 EA32 0.80 2018 JB3 0.88 2013 TQ5 0.89 (164294) 2004 XZ130 0.90 2006 WE4 0.93 2017 YH 0.94 2013 JX28 0.94 (413563) 2005 TG45 0.94 2006 KZ39 0.94 2015 ME131 0.95 2010 XB11 0.95 2014 FO47 0.96 (481817) 2008 UL90 0.96 2017 XA1 0.97 2012 VE46 0.97 (434326) 2004 JG6 0.97 (163693) Atira 0.98 Discovery of Apophis

● Most famous of the objects discovered during the search for Apohele ● Discovered 2004 June 19 UT ● Not a Subaru discovery, yet Subaru played a role that few people know about ● A stack of the three discovery images...

Apophis on 2004 June 19 UT

Subaru and Apophis

● UHAS55 identified as object of interest in Subaru images taken 2004 June 17 UT ● Motion faster than 90 arcsec/hr at solar elongation of 56 deg ● Attempted to recover on 2004 June 19 UT with Bok 2.29-m telescope on Kitt Peak ● Motion of 1.876 arcsec/min in RA and -0.629 arcsec/min in Dec ● UHAS58 moving 1.962 and -0.562 arcsec/min

Subaru and Apophis

● UHAS58 became 2004 MN4 and then the following year (99942) Apophis ● Apophis ephemeris for 2004 June 17 shows that Subaru missed discovering Apophis by 20 arcsec! ● Will approach Earth closer than geosynchronous satellites on 2029 April 13 (a Friday, no less) ● Orbit will be changed from Aten to Apollo variety

Impactor Table for Apophis

Recovery of Virtual Impactors

● A “virtual impactor” (VI) is an asteroid whose ephemeris uncertainty region sweeps over the Earth at some time in the next century ● Recovery shrinks the size of the ephemeris uncertainty region, usually eliminating the possibility of an impact for the next century

2002 EM7 is a Virtual Impactor

HSC ideal for 2002 EM7

Recovery of Virtual Impactors

● 2017 PY26 observed using queue mode on 2018 April 22 ● Clouds prevented reaching sufficient depth ● 2014 XM7 intended for 2018 May run did not execute ● 2014 GQ17 intended for 2018 June run did not execute

Planetary Satellites

● 20 new satellites of Saturn recently announced, 3 prograde, 17 retrograde ● Brings total number of known satellites of Saturn to 82, most of any planet (Jupiter has only 79) ● Observations made in 2004, 2005, 2006, and 2007 ● Probably all 20 new satellites are smaller than about 10 km diameter

S/2004 S24

● Discovered 2004 Dec 12 with Subaru

Beyond the

● Survey started by UH/IFA grads Scott Sheppard and using DECam on the CTIO Blanco 4-m telescope ● Northern hemisphere component added using HyperSuprimeCam on Subaru ● So far have covered about 3000 sq deg to fainter than 24th magnitude ● Responsible for discovering 75 percent of all known objects beyond 60 AU

Survey Coverage

Orbit of 2015 TG387

2015 TG387

● Numbered and now eligible for naming ● Have proposed the name Kuhonua ● Kuhonua is a life form mentioned in the Hawaiian creation chant, the Kumulipo; the name compares the orbit to the flight of migratory birds and evokes a yearning to be near the Earth.

Discovery of 2018 VG18 “Farout”

Orbit of 2018 VG18 “Farout”

Farfarout

● Distance record for 2018 VG18 “Farout” was short-lived ● Have now found an object around 133 AU ● Work in progress ● Most follow-up work done from Magellan

Orbits of Detached Objects

Brightness of Planet X

Planet X

● If there is a massive object in the far, far outer , it is most likely to be faint, hence most likely to be discovered by Subaru