This image, taken by the Hubble Telescope in 2003 and 2004, is one of the clearest images we have of Ceres. When the Dawn spacecraft arrives there this spring, well finally know what the planetoid really looks like. In the late 1700s, astronomers wondered about the large gap between Mars and Jupiter. Bodes law predicted a planet should be there, and in 1801, scientists finally found one... sort of. For half a century, Ceres was classified as a planet. Then, as telescopes became better, scientists found a number of smaller objects in a similar orbit. Collectively, those objects came to be known as the Asteroid Belt, and Ceres was reclassified as an asteroid. Ceres identity was called into question again in 2006, when scientists debated the status of Pluto and the definition of a planet. Planetary scientists like Sykes advocated for the name to apply to any object that has enough gravity to be round. The International Astronomical Union, however, defined a planet as something with enough gravity to clear everything out of its orbit. Pluto failed that test. And so did Ceres. “It would have been cool, because if Pluto were a planet, then Ceres would have to be, too,” says Sara Seager, a planetary scientist at the Massachusetts Institute of Technology. Ceres is, in a sense, a big, round, muddy time machine. Researchers are still splitting hairs over how to define a planet, but most agree that Ceres is likely a protoplanet—that is, an embryonic planet that got frozen in the early stages of development. By visiting Ceres, the Dawn mission hopes to understand more about how planets form, and what conditions were like in the early days of the solar system. It is, in a sense, a big, round, muddy time machine. The Dawn mission team is eager to see how Ceres compares to Vesta, another large asteroid/small protoplanet, which Dawn visited in 2011. Vesta is dry and rocky, like the inner planets of the solar system, whereas Ceres is more like the icy objects of the outer solar system. Studying both could reveal the processes that determine the fate of an infant planet. cratered surface of vesta The Search For Life Beneath its surface, Ceres may harbor a liquid ocean. Thats exciting for biologists who are looking for life on other worlds, because on Earth at least, everywhere theres water, theres life. Astronomers working on the Herschel Space Telescope in January 2014 reported detecting water vapor in a few patches around Ceres mid-latitudes. Something was spraying water into the air in very low yet detectable amounts. No one knows what the source is yet—it could be boring, such as ice sublimating into water vapor. But the universe is full of surprises, if the vapor jets of Enceladus and sulfur-belching volcanoes of Io are any evidence. Ceres could have cryovolcanoes that gush with water melted by the heat of radioactive decay deep below the planetoids surface. Dawn is currently the best—and only—means to find out more. “It certainly make Ceres interesting from an astrobiological view,” says NASA planetary scientist Chris McKay, whos not affiliated with the Dawn mission. Ceres might also harbor a lot of organic molecules. Combined with the water, radioactive heat, and other potential energy sources, including the Sun, Ceres is about as attractive a destination as an astrobiologist could hope for. These three things—organic molecules, water, and energy—are thought to be the crucial ingredients required for life to evolve. Small planets like Ceres and Pluto may be critical to understanding where life comes from and where life might be in the universe. The chances that life already exists on Ceres are probably very, very slim. Even if Ceres is a lifeless rock, however, the lessons to be learned would be priceless, says Rayman. On a world with all the necessary ingredients for life, for example, why could life not evolve? And what does that say about lifes chances elsewhere in the universe? If microbial beings do happen to live in Ceres inner ocean, Dawn isnt equipped to detect them. But the spacecrafts observations could influence NASA to select future missions with the capability to detect life. “If there is water under the surface, and its communicating with the surface through these cryovolcanoes, says Sykes, maybe we could send another mission to scoop up some water and ask, Are there any dead bugs here? Small and icy worlds like Ceres vastly outnumber Earth. In fact, theyre the most common types of planet-like bodies in our Solar System—and possibly the universe. “If the ice melts, would life evolve in that region?” Sykes asks. “Could these be incubators of life in the universe? I think these small planets, like Ceres and Pluto, may be critical to understanding where life comes from and where life might be in the universe.” What Lies Ahead The Dawn spacecraft launched Sept. 27, 2007. Since then, it has been moving in a spiral trajectory toward the outer solar system. It reached the protoplanet Vesta in July of 2011, and studied it for fourteen months. Now, the spacecraft is about to reach its ultimate destination. Heres the plan once it arrives: March 6, 2015: Dawn arrives in orbit around Ceres. (Note: Scientists dont know the exact nature of Ceres gravity, and since gravity will affect the spacecrafts travel time, all subsequent dates are estimated.) April 23, 2015: The spacecraft initially orbits at 8,400 miles above Ceres. Here it starts taking pictures, analyzing the planetoids surface, and looking for evidence of water vapor. June 10, 2015: Dawn descends to an altitude of 2,730 miles for a closer look. Aug. 15, 2015: From an altitude of 910 miles , Dawn extensively maps the surface of Ceres. It snaps photos from different angles, allowing researchers on Earth to gradually build a 3-D view of the landscape. Dec. 20, 2015: Dawn moves in to its closest orbit, just 230 miles above the surface—nearly 40 times nearer than its first orbit. “It will be like looking at a soccer ball seven inches from your eyes,” says Rayman. From here, Dawn takes more detailed observations. It maps Ceres gravity field, which should reveal how its mass is distributed in the interior (and possibly reveal a subsurface ocean). The spacecraft will also use gamma ray and neutron spectrometers, which measure the signature emissions from different elements in Ceres crust and interior. This will tell us what Ceres is made of. June 2016: The mission ends. Though Dawns fuel and solar panels may keep it alive for a few additional years, the spacecraft could continue to orbit Ceres for hundreds of years.
Posted on: Sun, 25 Jan 2015 04:57:40 +0000
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