火星と木星の間にある準惑星「ケレス」に、正体不明の白い点が見つかり、アメリカ航空宇宙局（NASA）の天文学者を困惑させている。
NASAは2月25日、ケレスの最新写真を公開。ケレスに接近中の探査機ドーンが19日、約4万6000kmの距離から撮影したものだが、ケレスの表面に白い点が2つ、くっきりと写っていた。
ドーンがケレスに接近した1月末以降、ケレスの表面には複数の白い点が見え始めたが、その正体をめぐって、専門家の間で「凍った湖」「クレーター」「山」などと意見が割れている。
カリフォルニア大学ロサンゼルス校（UCLA）で「ドーン」のプロジェクトを担当している主任研究員クリス・ラッセルさんは「ケレスの光る点は、同じクレーター内の盆地上に少し暗いもう一つの点を伴っています。これは火山のような物に由来する可能性がありますが、もっと解像度の高い写真が撮影されるのを待つ必要があります」と話している。
ドーンは3月6日にケレスの周囲を回る軌道に入る予定だ。
小惑星の画像集
Asteroid Ida and Its Moon(01 of07)
ガリレオ探査機が撮影したイダと衛星ダクティル(右の点)\n (credit:Wikimedia)
NEAR Space Probe to Land on Asteroid Eros(02 of07)
385446 01: FILE PHOTO: An image mosaic of the asteroid Eros, with sunlight coming from the northeast, taken by the robotic NEAR Shoemaker space probe March 3, 2000 from a distance of 204 kilometers, or 127 miles. After a year of circling and taking pictures, NEAR will touch down on asteroid Eros February 12, 2001, to capture surface details, which will be the first time any craft has tried to land on a tumbling space rock. (Photo Courtesy of NASA/Newsmakers) (credit:Getty Images via Getty Images)
Asteroid (253) Mathilde(03 of07)
NEAR captured this photo of asteroid 253 Mathilde on June 27, 1997; Mathilde was the target of a flyby encounter nearly three years before the mission went on to orbit asteroid 433 Eros. This image has been artificially colorized to match its likely appearance to a human observer. As a C-type asteroid, Mathilde is very dark, darker than asphalt. It is 59 by 47 kilometers in diameter.\nCredit: NASA / JHUAPL / Cornell / colorized image by Daniel MacháÄek (credit:Emily Lakdawalla, Planetary Society Blogger/Flickr)
Ida and Gaspra(04 of07)
This picture shows the asteroids Ida (left) and Gaspra (right) to the same scale. These images were taken by the Galileo spacecraft while enroute to Jupiter. Gaspra was imaged on October 29, 1991 at a range of 3,300 miles (5,300 km). Ida was imaged on August 28, 1993 from a range of 1,900 to 2,400 miles (3,000 to 3,800 km). Both objects are irregular in shape. Gaspra is about 10.5 miles long (17 km), and Ida is 18.6 miles long and 6 to 8 miles wide (9.3 x 12.7 x 29.9 km). These asteroids are just two of the billions of such rocky and metallic objects that orbit the sun mainly between Mars and Jupiter. A small percentage orbit near the other planets. The irregular shapes of these objects suggests that they are "chips" derived from larger bodies by catastrophic collisions between asteroids. The surface of Ida and Gaspra are peppered by small craters, evidence of much smaller collisions. Craters are more abundant on Ida, thereby suggesting that it formed earlier than Gaspra. Both asteroids have linear depressions over a thousand feet wide in places and a hundred feet or so deep; these depressions may be where loose fragmental soil (the "regolith") has partly drained into fractures. These asteroids show evidence of having such a fragmental layer, which on Ida may be 165 to 330 feet (50 to 100 m deep). The fragmental debris layers on asteroids may one day prove invaluable to space miners, who may obtain asteroids everything from precious metals for use on Earth to water destined for use in space. Asteroids are also important to life on Earth because sometimes their orbits wander across Earth\'s and collisions ensue. About 2,000 asteroids larger than 0.6 miles across presently have orbits that cross or come close to Earth\'s orbit. Impacts with objects as large as Gaspra and Ida are very rare, but they have occurred in the past and are capable of causing mass extinctions of almost everything that lives on our planet. \n\nImage Credit: NASA/JPL/USGS\n\nView Original Image\n\nVisit the NASA APPEL website. (credit:NASA APPEL/Flickr)
BENNUâS JOURNEY(05 of07)
Asteroid Bennu is a time capsule, containing the raw ingredients of the solar system.\nBennu has settled in a near-Earth orbit.\nToday, a NASA spacecraft OSIRIS-REx is going to retrieve a sample to learn more about our Solar Systemâs history.\n\n\nOSIRIRS-REx is a NASA sample return mission to visit Asteroid Bennu. We plan to grab a piece of Bennu, because itâs a time capsule that can tell us about the origins of our planet and our entire solar system.\n\nWatch the full video: youtu.be/gtUgarROs08\n\nLearn more about NASAâs OSIRIS-REx mission and the making of Bennuâs Journey: www.nasa.gov/content/goddard/bennus-journey/\n\nMore information on the OSIRIS-REx mission is available at:\nwww.nasa.gov/mission_pages/osiris-rex/index.html\nwww.asteroidmission.org\n\nNASA image use policy. \nNASA Goddard Space Flight Center enables NASAâs mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASAâs accomplishments by contributing compelling scientific knowledge to advance the Agencyâs mission.\nFollow us on Twitter\nLike us on Facebook\nFind us on Instagram (credit:NASA Goddard Photo and Video/Flickr)
Asteroid Gaspra from Galileo(06 of07)
Credit: NASA / JPL / Daniel MacháÄek (credit:daniel_machacek/Flickr)
Itokawa (ISAS, JAXA) - 02(07 of07)
(credit:Banco de Imágenes Geológicas/Flickr)
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