At a measly 2 kilometres in diameter, the smallest of two moonsrecently discovered orbiting Jupiter may be the giant planet'ssmallest known satellite. In September of 2010, two previouslyunknown distant satellites of Jupiter were discovered duringroutine tracking observations of already known moons. Thesediscoveries were then re-observed several times during the fall, inorder to determine that they were indeed satellites of Jupiter,leading to them obtaining MPC designations S/2010 J 1 and S/2010 J2 on the 1st of June 2011. With Jupiter now having 67 known satellites, the discovery of twotiny satellites does not have a large bearing on our understandingof the system. Information on the discoveries, the tracking effort, and newresults are provided below. A paper by Alexandersen et al.detailing the discovery and tracking of the two moons has beenaccepted for publication in the Astronomical Journal, forpublication in summer 2012. Discoveries S/2010 J 1 was discovered on images taken at the Palomar 200 inchHale Telescope on the 7th and 8th of September 2010, by aninternational team (NASA Jet Propulsion Laboratory (JPL)astronomers Robert Jacobson and Marina Brozovic, and University ofBritish Columbia astronomy professor Brett Gladman and Ph.D.student Mike Alexandersen). S/2010 J 2 was discovered on the 8th of September 2010 on imagestaken with the MegaCam mosaic CCD camera at the 3.6mCanada-France-Hawaii telescope (CFHT) by CFHT executive directorand director Christian Veillet. Upon later inspection, S/2010 J 2was also weakly visible in the September 7th images from Palomar. Follow-up observations Since discovery, the team has dedicated several hours of observingtime to tracking these satellites. Observations from October andNovember 2010 and January 2011 allowed the orbits to be determinedwell enough to confirm that they were indeed satellites and notjust nearby asteroids, allowing IAU designation in June 2011(discovery announcement from Minor Planet center here). Further follow-up observations in July, August, September andOctober 2011 (here and here) have fine-tuned the orbitdetermination for these satellites sufficiently that their positioncan reliably be predicted several years into the future. Precoveries During 2003 two large project (one by Brett Gladman and UBCpost-doctoral fellow Lynne Allen) observed the entire region aroundJupiter in a search for moons, also using CFHT. In the 2003observations, several faint objects were detected that were neverclassified as satellites because they were not recovered infollow-up observations in different months (needed to confirm thatthe orbit is indeed around Jupiter). However, with well determined orbits of S/2010 J 1 and S/2010 J 2,it was possible to extrapolate backwards in time to 2003.Alexandersen searched the 2003 images and confirmed that S/2010 J 1was indeed visible on several images. "We had actually already reported measurements of the first moonfrom Feb. 27 and 28, 2003 to the Minor Planet Center eight yearsago", said Gladman, "but observations over several months arerequired to prove that the object is orbiting Jupiter, and thismoon was too faint for the 2003 surveys to consistently track."Measurements of these images has increased the arc of measurementsof S/2010 J 1 from one to over eight years, making its orbit verywell determined. Unfortunately, S/2010 J 2 could not be located or seen in any ofthe 2003 images. However, this is not surprising, as S/2010 J 2 isthe faintest Jupiter satellite observed to date, so idealconditions are required to see it, even with CFHT. Characteristics and origin Based on their brightness, the size of the moons can be estimated.S/2010 J 1 is estimated to be ~3 km in diameter, while S/2010 J 1is estimated to be just ~2 km in diameter. It is believed thatnearly all moons the size of S/2010 J 1 or larger are known, butbecause there are always a lot more small moons than large moons,there must be dozens of satellites in the 1-3 km class; ourunplanned chance discovery of two such objects confirms thishypothesis. In addition to this, S/2010 J 2 is the faintest (and thus probablysmallest) Jovian satellite discovered to date, confirming that theJovian satellite population does continue down to those sizes. "It was exciting to realise that this [S/2010 J 2] is the smallestmoon in the Solar System that was discovered and tracked fromEarth," says Alexandersen. S/2010 J 1 is on an orbit with average distance (semi-major axis)from Jupiter of 23.45 million kilometres and orbital period of 2.02years. S/2010 J 2 has a semi-major axis of 21.01 million kilometresand an orbital period of 1.69 years. The irregular satellites of the giant planets are clustered in"families" with similar orbits and colours. These families arebelieved to have formed as a result of ancient collisions ofpassing-by comets or asteroids with former larger moons. S/2010 J 1appears to belong to the Carme group, while S/2010 J 2 appears tobelong to the Ananke group. I am an expert from womens-cottontights.com, while we provides the quality product, such as Womens Cotton Tights , China Knitted Leg Warmer, Children's Cotton Tights,and more.
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