Sedna (minor-planet designation 90377 Sedna) is a dwarf planet in the outermost reaches of the Solar System discovered in 2003. Spectroscopy has revealed that Sedna's surface composition is largely a mixture of water, methane, and nitrogen ices with tholins, similar to those of some other trans-Neptunian objects. Its surface is one of the reddest among Solar System objects. Sedna, within estimated uncertainties, is tied with as the largest planetoid not known to have a moon. It has a diameter of approximately 1,000 km (most likely between the sizes of the asteroid Ceres and Saturn's moon Tethys), with an unknown mass.
Sedna's orbit is one of the largest in the Solar System other than those of long-period comets, with its aphelion (farthest distance from the Sun) estimated at 937 astronomical units (AU). This is 31 times Neptune's distance from the Sun, and well beyond the closest portion of the heliopause, which defines the outer boundary of interplanetary space. , Sedna is near perihelion, its closest approach to the Sun, at a distance of , almost three times farther than Neptune. The dwarf planets and are presently further from the Sun than Sedna. An exploratory fly-by mission to Sedna at perihelion could be completed in 24.5 years using a Jupiter gravity assist.
Sedna has an exceptionally elongated orbit, and takes approximately 11,400 years to return to its closest approach to the Sun at a distant 76 AU. The IAU initially considered Sedna a member of the scattered disc, a group of objects sent into highly elongated orbits by the gravitational influence of Neptune. However, several astronomers contested this classification, because its perihelion is too large for it to have been scattered by any of the known planets. This has led some astronomers to informally refer to it as the first known member of the inner Oort cloud. It is the prototype of a new orbital class of object, the sednoids, which include and Leleākūhonua.
Astronomer Michael E.
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Following the discovery of the planet Neptune in 1846, there was considerable speculation that another planet might exist beyond its orbit. The search began in the mid-19th century and continued at the start of the 20th with Percival Lowell's quest for Planet X. Lowell proposed the Planet X hypothesis to explain apparent discrepancies in the orbits of the giant planets, particularly Uranus and Neptune, speculating that the gravity of a large unseen ninth planet could have perturbed Uranus enough to account for the irregularities.
Eris (minor-planet designation 136199 Eris) is the most massive and second-largest known dwarf planet in the Solar System. It is a trans-Neptunian object (TNO) in the scattered disk and has a high-eccentricity orbit. Eris was discovered in January 2005 by a Palomar Observatory–based team led by Mike Brown and verified later that year. In September 2006, it was named after the GrecoRoman goddess of strife and discord. Eris is the ninth-most massive known object orbiting the Sun and the sixteenth-most massive overall in the Solar System (counting moons).
Nemesis was a hypothetical red dwarf or brown dwarf, originally postulated in 1984 to be orbiting the Sun at a distance of about 95,000 AU (1.5 light-years), somewhat beyond the Oort cloud, to explain a perceived cycle of mass extinctions in the geological record, which seem to occur more often at intervals of 26 million years. In a 2017 paper, Sarah Sadavoy and Steven Stahler argued that the Sun was probably part of a binary system at the time of its formation, leading them to suggest "there probably was a Nemesis, a long time ago".
Explores the classification and statistics of AGN, black holes, unified AGN model, variability, megamasers, orbital motion measurement, and time-delay cosmography.
Super junctions (SJs) have enabled unprecedented performance in Silicon power devices, which could be further improved by applying this concept to wide bandgap semiconductors like gallium nitride (GaN). Currently, polarization super junctions (PSJs) are th ...
2022
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Despite their irresistible success, deep learning algorithms still heavily rely on annotated data, and unsupervised settings pose many challenges, such as finding the right inductive bias in diverse scenarios. In this paper, we propose an object-centric mo ...
We use our new light curves, along with historical data, to determine the rotation state, photometric properties, and convex shape models of the targets of the Lucy mission (3548) Eurybates and (21900) Orus. We determine a retrograde spin for both targets, ...