Bakersfield Night Sky — October 5, 2024
Beginning last weekend, Earth has a second moon. Alas, it is to be but for just a short time! It is a small near-Earth asteroid about 10 meters across that was discovered in early August by the “Asteroid Terrestrial-impact Last Alert System”, a telescope array in South Africa. It has an orbit that sometimes brings it near Earth and lingers for a bit before wandering off again. With this encounter it will linger until late November. The “mini-moon” is much too small and far away to see with any telescope smaller than 30 inches in diameter and then only with a good CCD detector and extended exposure to make it appear as just a dim dot.
This mini-moon has an exciting name: “2024 PT_5”. It is one member of five near-Earth asteroids (detected so far!) that have orbits bringing them near enough to become temporary satellites of Earth. The orbit is called a horseshoe type of orbit because relative to the Earth-sun line, it traces out a complex weaving in-and-out of Earth’s orbit around the sun. Because 2024 PT_5 has an orbit speed around the sun nearly the same as Earth’s, the times between getting close enough to Earth to become a temporary moon is measured in decades. It’s like two cars on a racetrack, with one going 60.0 mph and the other 60.1 mph—it’ll be a number of loops around the track before the faster car can pass by the slower one again. 2024 PT_5 will get close enough to Earth to become a mini-moon again in 2055 for about a month. The near-Earth asteroids might be future sites for space-mining in the future.
The launch window for NASA’s Europa Clipper mission to Jupiter’s moon Europa opens up on October 10. It will be the first mission that will be exclusively focused on studying Europa, a moon slightly smaller than our moon but is suspected to have a salty ocean below its icy surface with twice as much water as all of Earth’s water combined.
In the 1990s, the Galileo spacecraft flew by Europa twelve times as it explored Jupiter and its other large satellites. Galileo’s detailed images of Europa’s surface showed giant blocks of ice that appear to have been broken off and floated away into new positions, similar to what we see with the sea ice of the Arctic Ocean. Europa has no impact craters which means its surface is continually resurfaced to erase the craters, probably by liquid water welling up through the myriad cracks on its surface. Galileo also found that Jupiter’s magnetic field changes near Europa in a way most easily explained by the magnetic field creating an electrical current in a salty water ocean below Europa’s surface, that in turn creates a small magnetic field itself. Finally, the amount of tidal flexing Europa experiences in Jupiter’s enormous gravity field is enough to keep some of Europa’s water in a liquid state, even though Europa is five times farther from the sun than we are.
Europa very likely has the building block elements of life: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur—elements we find in a lot of other places in the universe but have they combined to make the complex organic compounds that life would need? Europa Clipper will look for them as it swings by Europa many times as the spacecraft orbits Jupiter. Because Europa is so close to Jupiter, it would take a huge amount of fuel to slow down a spacecraft enough for Europa’s weak gravity to snatch it away from Jupiter’s gravitational grip and have the spacecraft orbit Europa instead of Jupiter. In addition, Europa is right in the midst of Jupiter’s powerful radiation belts of Jupiter’s inner magnetic field, so all of the charged particles would quickly fry the electronics of a spacecraft orbiting Europa. The Europa Clipper’s orbit around Jupiter will be a huge looping one that makes only brief forays into the harsh radiation environment to scan Europa. The current mission plan is for nearly 50 flybys of Europa in a three-year period but if the electronics and funding last, there could be mission extensions allowing more flybys.
In addition to a sophisticated suite of nine instruments, Europa Clipper also carries a triangular vault plate made of tantalum metal with engravings of audio waveforms of the word “water” spoken in 103 languages on one side and on the reverse side, engravings of an original poem by U.S. Poet Laureate Ada Limón titled “In Praise of Mystery: A Poem for Europa” in the poet’s handwriting, the Drake Equation (calculating the number of communicating extra-terrestrial civilizations possible in the Milky Way) in Frank Drake’s handwriting, a representation of the hydrogen and hydroxyl (H-OH “water hole”) radio emission lines, and a tribute to planetary scientist Ron Greeley as well as a chip etched with 2.6 million names from NASA’s Message in a Bottle campaign.
Last Wednesday, October 2, the new moon was lined up with the sun but at the apogee point of its orbit to produce an annular solar eclipse visible in the southern Pacific and the southern tip of South America. Tonight a thin waxing crescent moon will be next to bright Venus. Two weeks later on the night of October 16/17, the full moon will be at the perigee point to make it be the closest supermoon of the year, 76 miles closer than last month’s supermoon.
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Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com
