Members of our solar system that were little more than points of light for decades or centuries have now become familiar family members, seen up close and personal by spacecraft. Here are introductions to three worlds that are no longer mere names in a catalog. Even the names of members in this trio may be unfamiliar to some. They’re worth getting to know.
Vesta: At long last, after its launch four years ago, the DAWN spacecraft is in orbit around Vesta – second largest of the asteroids. Having been in orbit now for 3 months (7/29/2011), DAWN has given scientists enough material to share initial science results (to say nothing of eye-popping images). In its Oct. 3 report, accompanied by a false-color image of the asteroid, Science Daily headlined the highlights as “Massive Mountains, Rough Surface, and Old-Young Dichotomy in Hemispheres.” Science Daily posted more information on Oct. 14, but the BBC News beat them by a day. JPL’s DAWN mission site is the place to look for official press releases and news.
Most amazing is a south polar mountain three times the height of Everest – one of the largest mountains in the solar system, here on a body smaller across than Texas. The mountain,13 miles higher than surrounding terrain, sits in a large impact basin named Rhea Silvia. It is just 3 miles shy of the record holder on Mars, Olympus Mons. National Geographic News posted an oblique view of the massive mountain. Sporting equatorial troughs and other large impact basins,Vesta had another surprise reminiscent of some of the outer-planet moons like Enceladus and Miranda: parts that look old (according to crater counts, see 4/13/2011), and parts that look young (see Astronomy Picture of the Day for August 2, 2011). Planetary scientists may have to concoct a new word like yold for this oxymoronic dichotomy. Vesta is rocky; Ceres, the largest asteroid, is icy. It will be interesting to compare these two giants among mini-worlds after DAWN arrives at Ceres in 2015.
Lutetia: The 21st asteroid discovered is named Lutetia. In July 2010, the European Space Agency’s Rosetta spacecraft, on its way to an epic landing on comet Churyumov-Gerasimenko in 2014, flew by the asteroid and took images and data. Three papers in Science this week (28 Oct 2011, doi:10.1126/science.1207325) provided the first anaylsis from the encounter. “Lutetia has a complex geology and one of the highest asteroid densities measured so far,” the papers said: some 3.4 grams per cubic centimeter. This is leading some of the scientists to hypothesize that Lutetia represents a primordial planetesimal that never coalesced into a planet. “This contrasts with smaller asteroids visited by previous spacecraft, which are probably shattered bodies, fragments of larger parents, or reaccumulated rubble piles,” the scientists said. While viewing a photo of Lutetia and other visited asteroids and comets on Astronomy Picture of the Day for 7/26/2010, readers may wish to puzzle between Science Daily’s headline that Lutetia is a prehistoric relic, and PhysOrg’s that it may have a warm core. Be sure to watch the short flyby animation on PhysOrg.
Eris: This is the only body of the three not visited by spacecraft, but it made the news because revised measurements make it about the same size as Pluto. When first discovered by Mike Brown in 2005, it was thought to be larger than Pluto, and led to an emotional debate about what defines a planet. Both Pluto and Eris were re-classified by the International Astronomical Union (IAU) as “dwarf planets” as scientists realized that many more such bodies might exist in the Kuiper Belt, a region beyond Neptune. Like Pluto, Eris has a moon (though Pluto now boasts four); its name is Dysnomia. The two are the most distant objects visible in the solar system. Nature this week announced new estimates for Eris’s size, based on a recent stellar occultation that constrains its radius to 1,163 km – in the ballpark of Pluto. This led popular science sites like Science Daily to announce that “Pluto has a twin.” Live Science posted an artist’s conception, a four-minute animated video from ESA with dramatic visuals, and a description of the stellar occultation method used. The smaller radius means Eris is surprisingly bright. Some scientists interpret this to mean Eris has a collapsed, frozen atmosphere on its surface, while Pluto still has a thin atmosphere. Amanda Gulbis wrote in Nature (27 Oct, pp. 464-465, doi:10.1038/478464a), “This unusually bright surface is difficult to reconcile with the idea that objects in the outer Solar System become darkened by cosmic rays and micrometeorite impacts over time.”
The space program is not dead; some of the best discoveries are being made by robotic spacecraft that continue the reconnaissance of our sun’s back yard. Each new body examined presents surprises. Surprises lead planetary scientists, who never predicted such things, to speculate. Speculation is built on assumptions. One assumption is that small things build big things (the bottom-up philosophy); this fits well with evolution. What we observe, though, is collisions breaking things into smaller pieces – a top-down philosophy. Calling Lutetia a primordial planetesimal does not make it one. National Geographic headlined that Eris “Has [a] Frozen Atmosphere,” but that was an interpretation, not an observation.
As reported here, planetary scientists have an awful time building up large bodies out of dust and gas, sometimes resorting to miracles to make it happen (8/21/2009). Whenever their bottom-up philosophy needs a miracle of creation, like our life-assisting moon (9/17/2010), or an ocean (10/11/2011), they send in an unobserved impactor to perform the miracle. Top-down models that begin with intelligent design have no need of such ad hoc lucky strikes. (Notice that everyone believes in miracles; some ascribe them to chance and accident, others to purpose and planning.) Take a little walk on the planet under your feet on a calm day at sunset and ask if it looks accidental.
By the way, Comet Elenin, an object many wrongly feared to be a doomsday bullet that was going to kill us, broke up as it flew safely out of reach of Earth, and is now vanished and forgotten (Science Daily). That’s a lesson on not being taken in by fear-mongers, but also provides another case of solar system bodies breaking up, not building up.