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Astro Update, February 2019

Selected Summaries of Space News

by Don Lynn

Kuiper Belt Object Flyby

On December 31st, New Horizons (Pluto spacecraft) flew by the Kuiper Belt object 2014 MU69, since unofficially named Ultima Thule, at a distance of only 2200 miles, fervently taking images and other data. This was the farthest-from-Earth spacecraft encounter with any celestial body.

Ultima Thule turns out to be a contact binary, that is, two roughly spherical bodies barely in contact with each other. The larger, “Ultima,” is about 12 miles across, while the smaller, “Thule,” is about nine. It’s thought that the two bodies came together early in the history of the solar system. The “crash” must have occurred at the speed of a walk, in order for them to have stuck with little damage.

The object is probably mostly water ice, though the surface is fairly dark (about as dark as our Moon’s dark markings) and reddish, as is common for ice with mixed-in carbon compounds that have been exposed to space radiation for a long time. The area around the neck joining the two pieces is considerably lighter-colored, possibly consisting of small particles pulled there by gravity. The object rotates in about 15 hours.

Ultima Thule was discovered about eight years after New Horizons was launched, during an extensive search for any other object nearing the spacecraft’s trajectory after its Pluto encounter. This is the only case in history of a spacecraft’s target being discovered after launch. Because New Horizons is expected to operate for many more years, the spacecraft team will soon apply for telescope time (Hubble and ground-based) to search for another target in the Kuiper Belt that will be near the current trajectory. The telescopic camera onboard New Horizons will also be used in the search. In the meantime, the data collected during the flyby will take about 20 months to transmit back to us, since a small radio at a great distance must transmit very slowly to be received flawlessly.

Lunar Rover Landed

On January 2nd, the Chinese space agency soft-landed the spacecraft Chang’e 4 (named for a Chinese Moon goddess) on the far side of our Moon, a first. It deployed a rover called Yutu-2 (named after Chang’e’s mythical pet rabbit). The lander and rover took pictures of each other, as well as a panorama of the landing area. They landed in von Kármán Crater, which lies within the South Pole-Aitken Basin, one of the few lava-filled plains (“seas”) on the far side. In addition to the usual cameras and spectrometers, the lander and rover carry a ground-penetrating radar, a German-built particle detector, and a Swedish ion detector. The spacecraft have heating devices to protect them during the long lunar night, which lasts about 14 Earth days. Remember this: Chang’e 4 landed on the far side of the Moon, not the “dark” side, which exists only in a Pink Floyd song. (Some news reports by non-scientists keep getting this wrong.)

Black Hole Mergers

The LIGO team has announced a total of 10 detections of gravitational waves caused by mergers of black holes, and several more “maybes” (events on the edge of detectability). All of the masses calculated for those merging black holes have been within the range theorists expect with the collapse of a massive star at the end of its life, that is, about 5-50 times the Sun’s mass.

It is somewhat of a mystery though, why the black holes detected by gravitational waves have tended to be at the top end of the mass range, while black holes found by telescopes (excluding the supermassive ones in the centers of galaxies) have tended to be at the low end of that range. One proposal is that some of the merging black holes are themselves products of mergers, and therefore more massive, but analysis of the spins of the merging black holes contradicts this. The product of a merger should have a huge spin, a large fraction of the maximum possible (limited by the speed of light). In fact, this has been true for the resulting black holes of the observed mergers. However, the individual spins of the 10 pairs of black holes before merging have been small, usually undetectably small.

Fast Radio Bursts

A new radio-telescope in Canada named CHIME has detected 13 fast radio bursts (FRBs). These bursts happen at random times and locations in the sky. Although FRBs occur all the time, radio-telescopes are almost never pointed at the right place and time to catch them, so only a few dozen have ever been seen. The bursts’ characteristics indicate that they have been traveling through at least millions of light-years of space, so their sources must be extremely powerful.

Before the CHIME data, only one FRB has ever been seen to repeat, but the new observations include the second known repeater. Both repeaters have been found to drift lower in frequency over time, but the underlying cause isn’t understood.

The 13 FRBs were detected in just three weeks, while CHIME was running at partial capacity—several are expected to be detected per day when CHIME is fully operational.

Water Found in Asteroids

Using a spectrometer on the AKARI infrared space telescope, researchers have detected hydrated minerals on a substantial number of asteroids. (Hydrated minerals have water trapped within them.) In the past, astronomers thought that asteroids were largely devoid of water, but the new study shows that the water is just locked up inside their rocks. This discovery was not possible before, because other infrared space telescopes have not had the particular wavelength range or sensitivity of AKARI. Of the 66 asteroids observed, 17 C-type (carbonaceous) asteroids were found to show the hydrated minerals, but only a few of the many observed S-type (siliceous) asteroids indicated the presence of water. This implies that C-type asteroids formed in a water-rich location and S-types did not. AKARI is no longer in service, so further observations will have to wait for the James Webb Space Telescope, now scheduled for 2021.

Gem Planets

Several years ago, astronomers announced that one of the planets orbiting star 55 Cancri was likely made partly of diamonds, since it contained substantial carbon and experienced high pressure and temperature. Further study of this and two similar planets has found that they have more aluminum and calcium than carbon, and that the aluminum and calcium are in the form of oxide compounds. (Maybe there is no diamond planet, but ruby and sapphire—forms of aluminum oxide—planets instead.)

A planet with no iron core, and with much aluminum and calcium, matches what theorists say should happen when a planet forms in a very high temperature zone. Aluminum and calcium also match the densities of the three studied planets. The team involved in this latest study suggests that these represent a new class of planet.

Farthest Solar System Object Found

An object dubbed 2018 VG18, but nicknamed Farout, has been discovered at a distance of roughly 120 times the Earth’s distance from the Sun, making it the solar system body that’s farthest from us—at least for now. Other objects are known with orbits that will take them to greater distances than this, but they were all discovered (and are still) at nearer points in their orbits.

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