by Kim Malville
What is happening in the sky this month?
March 1-3: Jupiter, Saturn and Venus are lined up before dawn. The crescent moon becomes increasingly slender as it moves past these planets.
March 10: Start of daylight savings time.
March 11-13: After sunset, the crescent moon has moved from morning to evening and starts out close to Mars.
March 12: The moon moves next to the Hyades, the open star cluster in Taurus.
March 13: The moon continues moving upward, passing Aldebaran.
March 20: Spring Equinox occurs at 3:58 MDT. Celebrate the start of spring.
March 21: Try locating the zodiacal light in the west above the setting sun. It will appear as a faint pyramid of light passing through Taurus and perhaps into Gemini. It is produced by light scattered by dust particles lying in the plane of the planets.
A piece of Earth hit the Moon 4 billion years ago
A lunar rock, known at Big Bertha, collected by Apollo 14 astronauts in 1971, contains a 2 cm piece of rock with a chemical composition common to Earth and very unusual for the Moon. Although meteorites that have reached the earth’s surface have been found coming from Mars, the moon, and asteroids, this is the first time a rock on the moon has been identified as terrestrial in origin. The rock may have been thrown into space when an asteroid struck our planet about 4 billion years ago during the Hadean eon. That was a time of truly hellish conditions on the earth. It was still warm and was being battered by frequent collisions of debris left over from the formation of the planets. In addition, the moon at that time was about three times closer to the earth than it is now, gradually spiraling away.
The standard giant-impact hypothesis for the origin of the moon suggests that a Mars-sized body hit the Earth, creating a large debris ring around Earth. This collision also resulted in the 23.5°-tilted axis of the earth, thus causing our seasons. Some proportion of this ejecta escaped into space, but the rest consolidated into a single body in orbit about Earth, creating the Moon. The colliding body has been called Theia, the mother of Selene, the Moon goddess in Greek mythology. The moon is suspect to have been initially only 12,000 to 18,000 miles above the earth. Now it is 240,000 miles away. At such a small distance, the moon would have produced high tides on the partially molten Earth, causing the moon to spiral outward, rapidly at first and then slowing down. The moon now spirals outward at a rate of 1.6 inches a year. Sometime in the future, it will have moved so far away that we will no longer have solar eclipses!
The two men of the Apollo 14 lunar landing mission photographed and collected the large rock pictured just above the exact center of this picture. The rock, casting a shadow off to the left, has been named Big Bertha. It lies between the wheel tracks made by the so-called modular equipment transporter. A few prints of the lunar overshoes of the crew members are at the left. This photo was made near the boulder field near the rim of Cone Crater. It doesn’t seem so big in the photo.
The 2cm fragment in Big Bertha is similar to granite, which is extremely rare on the Moon but common on Earth. The age of the rock is about 4 billion years, formed in a watery environment corresponding to a depth of 12 miles. It’s a measure of how brutal conditions were on the earth during the Hadean epoch, that a collision tore a piece of rock from so deep in the earth.
The rock crystalized in the earth some 4-4.1 billion years ago, and sometime later it was excavated by a large impact and launched toward the moon. The oldest rocks on earth are metamorphic rocks from Canada and Greenland and have ages to this fragment of Big Bertha. Once the sample reached the lunar surface, it was thrown around by several other impact events, one of which partially melted it 3.9 billion years ago, and which probably buried it beneath the surface. The final impact to affect this sample occurred about 26 million years ago, when another asteroid hit the Moon, producing the 1,115-foot wide Cone Crater. That moved the sample back onto the lunar surface where astronauts collected it 48 years ago. What an amazing saga is was: tossed around for billions of years, finally finding a peaceful resting place on the surface of the moon, only to be picked up and carried back to earth to be prodded and analyzed in laboratories in Texas and Australia.
Actually, the real Big Bertha is a huge boring machine, more than 57 feet in diameter, used in Seattle and named after its first female mayor.
Ultima Thule is not a snowman
I have written about the New Horizons Spacecraft passing Ultima Thule during the past two months. I was really fascinated by this courageous endeavor. Now we have discovered that instead of being of a snowman, it’s a dented walnut and a pancake. After the spacecraft flew past its closest approach and was able to view the object from behind, its peculiar nature was revealed. The theorists were initially quite happy that blobs of spherical material were joined together to form a snowman. Their theories were apparently confirmed. Now, it’s back to the drawing board. “We’ve never seen something like this orbiting the sun,” Alan Stern, principal investigator on the New Horizons mission.” Eager to put a positive spin on this great surprise, he continued, “but more importantly, the new images are creating scientific puzzles about how such an object could even be formed.” It’s not really all that surprising. Debris left over after formation of the planets, moons, comets, and asteroids space could have been huge spinning droplets of slush with many shapes. Rapid spinning would flatten them. Only the larger objects like planets and the largest asteroids had to become spherical because of their self-gravity. Bits of data will continue to dribble in for another year and a half, and I hope we may be confronted with many more surprises.