Mysterious Dwarf Planet Ceres May Be Ripe for Life
NASA's Dawn mission is about to arrive in orbit around Ceres and the hunt for the dwarf planet's past (and possibly present) habitable potential is on.
Scientists have long suspected that Ceres, the largest object in the asteroid belt, had an underground layer of ice, the result of an ancient ocean that froze eons ago. But last month, as NASA's Dawn spacecraft neared the end of its 7.5-year journey to the dwarf planet, they were startled to find that something bright -- ice or salt perhaps -- was glinting on the surface.
"There's likely something that is highly reflective, or at least more highly reflective on the surface than the rest of the surrounding area," Mike Miller, vice president for science programs with satellite manufacturer Orbital ATK, told Discovery News.
"This could be fresh material that's just recently been brought to the surface, or it could have been an impact that brought certain chemicals to that particular crater," add Joe Makowski, Orbital's Dawn program manager.
Extrapolating from Ceres' round shape and relatively low density, computer models indicate Ceres has a rocky core and icy mantle, covered by a layer of dust, clays and deposits.
"Ceres is lighter than the rocky planets, meaning that it retained a lot of water and light volatile elements that were present in the solar nebula when Ceres was formed ... In contrast, bodies like the moon and (the asteroid) Vesta, have melted and boiled off the water and the light elements, leaving them dry and rocky," said Carol Raymond, Dawn deputy lead scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
That makes Ceres a lot like Europa and Enceladus, two of Jupiter's icy moons that are believed to harbor underground oceans.
With moderate heating from the decay of naturally occurring radioactive elements, "we expect that in the past that there was ocean in Ceres in contact with the rock beneath an ice cap," Raymond said.
And that raises the prospect that Ceres had conditions and chemistry suitable for microbial life to evolve.
"We expect that (Ceres) had astrobiological potential," Raymond told Discovery News.
A layer of liquid inside Ceres is unlikely today, but the 600-mile wide protoplanet promises surprises.
In addition to mysterious bright spots on its surface, Ceres may periodically release water vapor into space. Scientists theorize that impacting comets or asteroids may heat underlying ice, vaporizing some and leaving areas exposed to the surface.
"Perhaps we're seeing a deposit that was left behind which is rich in material like salt," Raymond said. "This feature is unique in the solar system."
And even though Ceres is unlikely to have an underground ocean today, there is evidence that its ice can move, providing a mechanism for minerals leached from rock to travel to the warmer surface.
NASA dispatched Dawn to Ceres in hopes of learning what role similar bodies played in the construction and evolution of Earth and its planetary neighbors. The spacecraft is scheduled to slip into orbit around Ceres on Friday.
Dawn previously spent 14 months surveying and mapping Vesta, the second largest body in the main asteroid belt, located between Mars and Jupiter.
It will take Dawn about a month to position itself for its primary science mission, which is scheduled to run through June 2016.
This artist's concept shows NASA's Dawn spacecraft arriving at the dwarf planet Ceres.
The term "dwarf planet" wasn't defined until the infamous International Astronomical Union (IAU) vote in 2006, but this year, 9 years later, we are beginning to get our first ever close-up views of two of our solar system's most famous dwarf planets: Pluto and Ceres.
Currently spiraling in on Ceres, the innermost dwarf planet inhabiting the asteroid belt between the orbits of Mars and Jupiter, NASA's Dawn spacecraft is slowly revealing a cratered and complex world, details of which that have so far eluded even Hubble's powerful vision. Dawn is scheduled to make final orbital insertion around Ceres in March 2015 where it is destined to remain after its fuel runs out as a permanent human-made satellite of Ceres. A comparison image of the Hubble and Dawn views of Ceres is shown above.
But Dawn is just the first dwarf planet encounter of 2015. In July, NASA's New Horizons mission will flyby Pluto and its system of moons, exploring the mysterious Kuiper Belt. Between Hubble's blurry observations of Ceres and Pluto and this year's NASA encounters, many artists' impressions of these enigmatic worlds have guessed at what lies in store for our robotic explorers. But how do they measure up now we are beginning to see Ceres' and Pluto's surfaces?
This artist's impression of Ceres shows NASA's Dawn spacecraft in orbit around the dwarf planet. As opposed to an ice encrusted world, this visualization shows a cratered, moon-like surface.
Again with Dawn in view, this artist's impression shows an active Ceres complete with water vapor escaping from a possible sub-surface ocean. Water vapor was detected in the vicinity of Ceres by Hubble, so Dawn will be on the look-out for any trace of geysers venting water.
As seen by Hubble from afar, curious white patches and possible variations in Ceres' surface composition can be seen. However, any detail in these images have so far prevented planetary scientists from fully understanding the dwarf planet's true nature.
But now, as Dawn fast approaches orbital insertion, we're being treated to a bounty of data that shows a possibly ancient, rocky surface. Those curious white patches originally spied by Hubble are also snapping into view -- but what are they? Theories abound, but they may be tentative signs of subsurface water escaping to space and freezing on the surface. These are all signs of cryovolcanism, a dynamic that may dominate dwarf planet surface morphology.
From afar, NASA's Dawn mission is able to watch Ceres rotate, as this series of observations on Feb. 4 shows.
As Dawn gets up-close and personal with Ceres, the drama in the outer solar system is only just beginning to unfold. After 9 years of flying toward Pluto, NASA's New Horizons mission has begun approach preparations for its flyby in July.
From ground-based and Hubble observations, there at tantalizing clues that this frozen world has a surprisingly dynamic surface with a thin atmosphere that changes during Pluto's 248 year orbit around the sun. In this artist's impression of New Horizons flying over Pluto, an atmosphere has been included with cryovolcanos -- the latter of which planetary scientists hope to confirm in July.
Pluto has a system of known moons, the largest of which, Charon, may be considered to be Pluto's binary partner. As Charon orbits Pluto, its powerful gravitational field tugs the dwarf planet off center, a dynamic that New Horizons has observed as it approaches.
This artist's conception shows Pluto's moon Charon eclipsing the dwarf planet. Twice every orbit around the sun, each world eclipses the other.
When Hubble spies on Pluto, it can see the different shades of the dwarf planet's surface rotate. As shown here in these blotchy images, little detail is obvious, but large regions with differing albedo (reflectiveness) may reveal huge craters, vast plains or mountains. But until New Horizons gets close, these regions will remain a mystery.
In this digital illustration rendered from 3-D NASA data of Pluto, an attempt has been made at matching observations with possible surface features.
In July 2014, NASA's New Horizons looked ahead and spied its ultimate goal: Pluto and Charon. Although tiny pinpricks of light, the pair can be seen orbiting one another in a binary dance that shifts Pluto off center. Both masses actually orbit an invisible point in space, above Pluto's surface, known as the Pluto-Charon barycenter. These observations have increased calls for Pluto to be redefined (yet again) as a 'binary planet.'
Having spotted Charon months ago, New Horizons is now beginning to see Pluto's wider family of moons pop into view. Shown here are moons Nix (yellow diamond) and Hydra (orange diamond).
Once NASA's New Horizons mission careens through the Pluto-Charon system, assuming it doesn't hit any debris on its way through, its mission in the Kuiper Belt has only just begun. Hubble is currently being used to identify possible icy targets
the spacecraft's Pluto encounter. Shown here is an artist's impression of another dwarf planet, Eris, that was discovered in 2005. Originally thought to be the
planet of the solar system, its discovery led to the IAU's decision to reclassify these small worlds as dwarf planets, demoting Pluto in the process, leaving us with 8 planets. But as we approach Pluto and begin to understand Ceres, just because they are dwarf planets doesn't mean they're not rich and dynamic places to explore. Our voyage of dwarf planet discovery has only just begun and regardless of our need to classify celestial objects, Pluto and Ceres hold some fascinating clues to planetary formation and solar system evolution.
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