Small bodies loom large

Posted by Alison Klesman
on Wednesday, October 18, 2017

Quasi-satellite 2016 HO3 orbits the Sun while also looping around Earth. The object appears to be in an orbit that will last for a few centuries. // NASA/JPL

By Richard Talcott

As their name implies, planetary scientists spend much of their time studying the biggest bodies in the Sun’s family: the planets and their large moons. But on Tuesday at the 49th annual meeting of the Division for Planetary Sciences in Provo, Utah, researchers turned some of their attention to the smaller bodies in our solar system.

Vishnu Reddy of the University of Arizona reported on his team’s observations of Earth’s quasi-satellite, 2016 HO3. Although the object orbits the Sun, it also makes a yearly loop around Earth on a path that ranges from about 38 to 100 times the Moon’s distance. Reddy’s team studied 2016 HO3 with the twin 8.4-meter mirrors of the Large Binocular Telescope in Arizona. The scientists found that it rotates once every 28 minutes, is no more than about 330 feet (100 meters) in diameter, and appears to be a normal asteroid, not some wayward piece of space junk. This is the sixth quasi-satellite discovered around Earth but appears to be the most stable, capable of surviving in this orbit for a few centuries.

Alan Harris of MoreData! in California has been looking at larger objects in the near-Earth population: those capable of inflicting significant harm on our planet. To estimate how many of these so-called potentially hazardous asteroids (those larger than 0.6 mile [1 kilometer] in diameter) exist, he needed to take into account how many have been found with the available technology in the sky areas observed. He concludes that about 921 such asteroids exist, of which 884 have been discovered so far. This means current surveys are 96 percent complete, and astronomers need to find only 30 to 40 more.

Panelists prepare to discuss their findings at Tuesday’s press conference at the Division for Planetary Sciences meeting. // Richard Talcott

Juliette Becker of the University of Michigan set her sights farther afield. She and her colleagues used computer simulations to show that the hypothesized Planet Nine would help stabilize trans-Neptunian objects (TNOs) in orbits more than 250 times the size of Earth’s circuit around the Sun (an astronomical unit, or AU). Such objects are subject to gravitational encounters that could fling them toward the Sun or eject them from the solar system entirely. The simulations show that a Planet Nine could stabilize TNOs through what the team calls “resonance hopping,” in which a TNO jumps between stable orbits. The process could keep such objects bound to the Sun for the age of the solar system. As Becker says, the simulation results are consistent with a Planet Nine, but not evidence for it.

The team also found a new TNO in a highly elongated, steeply inclined orbit at an average distance of 450 AU. The discovery came through observations made during the Dark Energy Survey, which uses a 4-meter telescope in Chile to conduct a deep, wide-field survey of the sky. The new object, as yet unnamed, should help narrow the sky area astronomers are searching to try to spot Planet Nine.

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