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DPS/EPSC update: 2007 OR10 has a moon!

Posted By Emily Lakdawalla

19-10-2016 11:46 CDT

Topics: trans-neptunian objects, Hubble Space Telescope, explaining science, dwarf planets beyond Neptune, conference report

All this week I'm attending the joint meeting of the European Planetary Science Congress and the Division for Planetary Sciences of the American Astronomical Society (DPS/EPSC), taking place here in Pasadena, California. There's a lot of science to digest but I can get a big piece of news out of the way quickly: the third-largest object known beyond Neptune, 2007 OR10, has a moon. The discovery was reported in a poster by Gábor Marton, Csaba Kiss, and Thomas Mueller on Monday.

A moon for 2007OR10

NASA / STScI / Wesley Fraser / Gábor Marton et al.

A moon for 2007OR10
The Hubble Space Telescope took this photo of 2007 OR10 on September 18, 2010. Later analysis of the images revealed the presence of a moon (red circle).

2007 OR10 has stood out as the largest known trans-Neptunian object lacking a Moon. Most of the other big worlds have at least one: Pluto has Charon, Styx, Nix, Hydra and Kerberos; Eris has Dysnomia; Makemake has one discovered this year; Haumea has Hi'iaka and Namaka; Orcus has Vanth; Quaoar has Weywot. Now Sedna is the largest known object out there for which we have not -- yet -- discovered a moon. (Hopefully somebody will look!)

With a slow rotation period of 45 hours, astronomers have suspected for a while that 2007 OR10 had a moon, whose tidal interactions with the primary would have been responsible for slowing its rotation. Marton et al report the discovery in a set of older Hubble WFC3 images taken in September 2010. The new moon likely has a diameter of roughly 300 kilometers (roughly Hyperion-sized), as compared to 2007 OR10's roughly 1575 kilometers (roughly Rhea-sized). Although 300 kilometers is fully 20% of the diameter of the primary, Marton and coworkers state that, given a likely very dark surface, it doesn't contribute enough reflected light to 2007 OR10's signal to affect diameter estimates for the larger body. It is also too far from the parent body for the two to be in mutually synchronous rotation.

Both Makemake and 2007 OR10's newly discovered moons need followup to better determine their properties and orbits. Alex Parker proposed to follow up Makemake with Hubble, but his proposal was declined; Marton and Kiss told me they have proposed to follow up OR10 with Hubble, but have not heard yet.

One thing we do know: when OR10 finally gets a name, it needs to be a name that allows for the easy generation of a companion name for its moon!

The original images were taken as a part of a large survey of trans-Neptunian objects by Wesley Fraser; the image I processed to produce the view above was IBJG01FMQ.

Many thanks to Alex Parker for pointing out this poster to me!

 
See other posts from October 2016

 

Read more blog entries about: trans-neptunian objects, Hubble Space Telescope, explaining science, dwarf planets beyond Neptune, conference report

Comments:

agmartin: 10/19/2016 12:53 CDT

"Now Sedna is the largest known object out there for which we have not -- yet -- discovered a moon. (Hopefully somebody will look!)" Or look again, HST looked in 2004. Perhaps a moon was missed, like with Makemake.

Charles Bell: 10/19/2016 04:15 CDT

Calibrated fits images for (225088) 2007 OR10 after cosmic ray strike rejection filtering can be found online https://archive.stsci.edu/missions/hlsp/mt/wfc3/12234_2007or10/ The image featured here is hlsp_mt_hst_wfc3-uvis_ibjg01fmq-2007or10_f606w_v1-0_sci.fits

some guy: 11/06/2016 11:28 CST

I just wish they would name 2007 OR10 already. I personally like Enyo because she was the sister of Eris and appeared next to her on Achilles' shield, and 2007 OR10 is similar in size and orbit to Eris. Enyo was the goddess of war, and just like Mars (the god of war) 2007 OR10 is a very red object. Also we could name 2007 OR10's moon Enyalius who was Enyo's son.

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