StarDate

Gene Cernan was the last American to walk on the Moon. As he prepared to leave it, he expressed optimism that his colleagues would return soon.

CERNAN: As I take man’s last step from the surface for some time to come, but we believe not too long into the future…

Well, it’s probably been a little longer into the future than Cernan expected, but NASA is preparing to send astronauts back to the Moon. The Artemis II mission is scheduled to launch in the coming weeks. It will carry four astronauts to the Moon. They won’t land, or even go into orbit. But it will be the first time anyone has come close to the Moon in more than half a century.

The astronauts will follow a looping path to the Moon. They’ll fly behind it, coming within about 6500 miles of the surface. The Moon’s gravity will sling them back toward Earth. They’ll splash down in the Pacific Ocean.

During the 10-day mission, the astronauts will check out all of the systems on the Orion spacecraft. They’ll also conduct a few experiments, and make some observations of the Moon.

Artemis II has been delayed by several years. Among other problems, during the unmanned Artemis I mission, in 2022, the life support system and heat shield didn’t work as planned.

Astronauts are supposed to land on the Moon during the next mission. Issues with the lander and other problems may delay that until 2028 or beyond – adding to the gap between moonwalks.

Script by Damond Benningfield

The Moon is a tale of two faces. The side we see – the nearside – features giant volcanic plains and a fairly thin crust. The far side features more mountains and craters and much thicker crust. And the differences might go even deeper. The layer below the crust – the mantle – might be cooler on the farside – or was cooler billions of years ago.

That difference is suggested by samples returned to Earth by a Chinese lander – the first samples from the farside. Some of the samples formed from molten rock. It cooled and solidified 2.8 billion years ago, deep inside the Moon. Details about the samples suggest the molten rock was much cooler than the same layer on the nearside – by about 200 degrees Fahrenheit.

That’s probably because the far side has fewer radioactive elements, which heat the interior as they decay. Just why that’s the case isn’t clear. A smaller moon might have splatted into the lunar farside when the Moon was young. Or a giant asteroid impact might have moved things around. The pull of Earth’s gravity might have played a role as well.

Whatever the cause, there’s a big difference in the lunar hemispheres – which may be more than skin deep.

The gibbous Moon is passing through the constellation Taurus tonight. Aldebaran, the bull’s eye, is to the right of the Moon at nightfall. And Elnath, at the tip of one of the bull’s horns, is closer to the lower left of the Moon.

Script by Damond Benningfield

In Greek mythology, Chiron was the wisest of the centaurs – creatures who were half human and half horse. He taught other centaurs about medicine, botany, and other sciences.

Today, the astronomical Chiron is teaching scientists about the formation and evolution of ring systems.

Chiron is one of about a thousand known centaurs – chunks of ice and rock between the orbits of Jupiter and Neptune. It’s one of the larger ones, at an average diameter of about 125 miles. Even so, it’s so far away that it’s tough to study. But it sometimes passes in front of a distant star. Such a passage allows scientists to measure its size.

It also allows them to study the space around Chiron. Rings cause the light of the background star to flicker. Observing that effect from different locations, and at different times, provides a profile of the rings.

A study last year reported some changes. Scientists already knew of three rings. The new study reported evidence of a fourth ring. It’s so far out that Chiron’s weak gravity might not be able to hold it. The scientists also found a wide disk of dust.

The rings and disk might be debris from a small moon, or the result of an outburst from Chiron itself. Chiron is moving closer to the Sun. As it warms up, it could produce more outbursts. So the system could undergo more big changes in the years ahead – teaching us much more about the evolution of rings around the small bodies of the solar system.

Script by Damond Benningfield

The realm of the giant outer planets is like a transit station for some smaller bodies. They come from beyond the orbit of Neptune, the solar system’s most remote major planet. And like passengers at a hub airport, their destinations are all over the map.

These objects are called centaurs. Like the half-human, half-horses of myth, they’re hybrids – they look like both asteroids and comets. Most of them are quiet chunks of rock and ice, like asteroids. But some have haloes or tails of gas, like comets.

Centaurs orbit the Sun between Jupiter and Neptune. And their orbits cross those of at least one of the giant planets. They’re small and far away, so they’re hard to find. Even so, astronomers have discovered about a thousand of them. And there could be as many as a hundred thousand that are at least a kilometer across.

Centaurs come from a belt of debris beyond Neptune. They’re nudged inward by Neptune’s gravity. None of them will spend more than a few million years in the realm of the giants, though. Instead, the gravity of the planets will give them a kick. Some will be booted out of the solar system. Others will be pushed into the inner solar system. And others will slam into a planet.

The biggest centaur is Chariklo. It’s about 160 miles in diameter, and it has a couple of rings. The first centaur ever seen, Chiron, also has rings. And it’s growing new rings even now. More about that tomorrow.

Script by Damond Benningfield

Many of the features on the Moon are named for astronomers. So are features on Mars and other planets and moons. And hundreds of asteroids are named for astronomers as well.

But you won’t find many features named for astronomers here on Earth. Quite a few streets and schools are named after them. But when it comes to major features, the list is pretty thin – especially in the United States. One of the few is Mount Langley, a 14,000-foot summit in California. It’s named for Samuel Pierpont Langley, who was a long-time director of the Allegheny Observatory.

To see more features named for astronomers, though, you need to head south – to Australia, New Zealand, and even Antarctica.

In Australia, for example, a river and an estuary are named for Thomas Brisbane, an early governor of the state of New South Wales. And so is the city of Brisbane, the capital of Queensland. In addition to his government duties, Brisbane was an astronomer. He set up Australia’s first major observatory.

In New Zealand, several peaks in a large mountain range are named for astronomers, including Galileo and Copernicus. And an entire range is named for Johannes Kepler.

In Antarctica, many features are named for James Ross, an early explorer. But Ross himself named several features for astronomers, including Cape Smyth and Mount Lubbock – down-to-earth features named for men who studied the stars.

Script by Damond Benningfield