by Kim Malville
Mercury, the fleet-footed god, the fastest moving planet in the solar system pops up in our southwestern skies about 30 minutes after sunset on February 15. It climbs in the sky for the next 11 days reaching its greatest elongation from the sun on March 26, when it will be 11° above the western horizon about 30 minutes after sunset. Mercury will be bright and conspicuous in the evening twilight, setting about one and a half hours after sunset. Don’t miss it. Catch it when you can. It will disappear next month on March 6.
Mars remains a prominent object throughout the month. It starts the month in the constellation of Pisces and moves eastward through Aires into Taurus. Mars will be close to the Pleiades next month.
Jupiter is a morning planet, rising in the east at 4am in the beginning of the month and then at 2:30am at the end of the month.
Venus, a brilliant object in the morning skies, rises at 3:30am at the start of the month. On February 18 there will be a spectacular conjunction with Saturn, with Venus some 80 times brighter than the ringed planet.
Ultima Thule: The latest space spectacular
Last month I described the events that led up to the flyby of New Horizons of this small object 4 billion miles from Earth. Now we have some pictures.
We have been waiting more than three weeks for the latest picture from New Horizons flyby of the Kuiper Belt object on January 1. For that time the space craft was hidden behind the sun. Finally, the picture was downloaded on January 25, displaying a strange object that has been hanging out at the edge of the solar system for 4.5 billion years, touched by only the faintest glimmer of sunlight. This photo was taken 7 minutes before its closest approach. It’s been described as a snowman, but its more like a tar baby. Its average reflectivity is 7%, darker than the moon (which reflects 12%of sunlight), only a little brighter than fresh asphalt (which reflects 4%). It has a slightly red color, which may be due to organic compounds. Ultima Thule is 21 miles long, twice the size of the nucleus of Halley’s Comet. If it were to pass in the inner solar system, it could be a spectacular comet.
These two lobes, one roughly three times the size of the other, must have been formed by a very gentle collision, coming together at very slow speeds—less than 1 mile or kilometer an hour. If you collided with another car at those speeds, you probably wouldn’t bother to contact your insurance agent.
These slow formation speeds help to validate a recently proposed model for the origin of planets and other object in our solar system, which is known as pebble accretion. The gas and dust left over after formation of our sun, came together as small pebbles, which were gradually pulled together by gravity.
The Asteroid Itokawa
If you want to see what those pebbles look like, consider the asteroid named Itokawa, which the Japanese space agency visited in 2005. It appears to be a loosely-held-together swarm of pebbles. The largest is a pebble 150 feet across, and many are a few feet across and even smaller. This asteroid demonstrates the difficulty of deflecting an asteroid from a collision with earth. It we were to hit it with a rocket, it would shatter into millions of small particles that would rain down on the earth.
Future, higher-resolution pictures of Ultima Thule may reveal it has a similar nature. Now we see a few large pits; the largest on the smaller lobe (the head of the snowman) is 4 miles across. There are smaller pits at the shadow line, which are 2000 feet across. We don’t know if they are impact craters, collapsed pits, or remnants of blow holes. Both lobes also show many intriguing light and dark patterns of unknown origin, which may reveal clues about how this body was assembled during the formation of the solar system. One of the most striking of these is the bright “collar” separating the two lobes, which could be fresh ice ground up by the collision of these two bodies. In fact, it may not be the result of the only collision. Note that the pit on the smaller object almost matches a circular area on the largest one. There may have been an initial bounce, resulting in the eventual joining together of the two bodies. We will know more in another month.