On a personal note, today is the 1^th anniversary of my wife and I moving into our house in Virginia! We had actually arrived in the state a month earlier but rented a place until the sellers moved out of the house, but we don’t count that. It’s been an interesting year, to say the least. It’s also never far from my mind that all y’all were instrumental in helping this happen, especially the paid subbies. Without that income we’d be sunk, so I truly appreciate your support. Thanks.

Over the weekend Saturn reached opposition, which means it’s opposite the Sun in the sky. That means several things: it rises at sunset and sets at sunrise, so it’s up all night, but it also means the Earth is directly (or very close to directly) between Saturn and the Sun, so we’re as close to the bigger planet as we’ll be all year. That means Saturn appears biggest through a telescope, and is at its brightest.

If you have access to a telescope, take a look! Even good binoculars might show it as being slightly elongated due to the rings. That’s definitely worth trying to see.

Saturn is high to the southeast around 10:00 p.m., so I’d go out around then or later to see it. I might even haul my own ‘scope out somewhere to spot it; there are too many trees in my yard to see it from home. But it’s worth it. Saturn through a telescope is always an amazing experience.

The European Space Agency mission BepiColombo is on its way to Mercury, the innermost solar system planet. It launched in 2018 and is taking a roundabout path to Mercury, passing Earth once and Venus twice in order to lose enough orbital energy to drop toward the Sun — Earth orbits the Sun at about 30 kilometers per second, so it has to lose a lot of that “sideways” velocity to get closer. By passing Earth and Venus it gave up some of its energy to the planets, dropping down. Those flybys were in 2020 and 2021.

By the time it got to Mercury’s orbital distance, though, it was then moving too slowly to enter orbit, so it let the tiny planet pass it, doing a gravitational assist (a slingshot maneuver) to steal some of Mercury’s energy to speed up. It has to do this six times to get enough speed to enter orbit around Mercury! This has been made even more difficult due to an issue with the main thrusters used to accelerate the spacecraft, which has meant the engineers on Earth have had to figure out a new trajectory to get BepiColombo to Mercury.

The fourth pass just occurred on September 4, 2024. BepiColombo passed an incredible 165 km above Mercury’s surface, a danged close shave (if you tried that at Earth our atmosphere would mess everything up, but Mercury has none to speak of). While the main scientific camera is still in its enclosure for safety until the spacecraft achieves orbit, there are several low-resolution (1024x1024) monitoring cameras that are used to take images of the spacecraft to make sure everything’s doing what it’s supposed to. The orientation of BepiColombo allowed them to see the planet as it passed, and ESA released four of the images. I want to highlight two of them.

Holy wow!

You can see a couple of spacecraft parts; the one on the left holds the medium gain antenna and on the right is a magnetometer, used to measure magnetic fields (and has to be away from the spacecraft to prevent interference).

Mercury is battered and cratered below. The big crater is called Vivaldi — craters are by convention named after artists, composers, and writers — and is what’s called a peak-ring crater; the inner ring is a series of tall mountain peaks (one part is broken, where lava flowed and buried the hills later). It’s not clear how rings like this form. When a huge asteroid impacts a planetary surface, the rock underneath actually liquefies, and flows away from the impact point. Sometimes it “splashes back”, forming a central mountain peak like with the lunar crater Tycho, similar to a drop of water hitting the surface of a glass of water and forming a blob as the water splashes back.

The ring is more complicated, obviously. The outer crater is over 210 km across, and those peaks several kilometers in height. That makes the impact on the same scale as the one that wiped out the non-avian dinosaurs on Earth 66 million years ago…but it’s not even in the top 20 biggest craters on Mercury. That planet has been through a lot.

The other image is just spectacular: a full-disk shot showing just how cratered the planet is:

The south pole is near the top of the planet in this angle, just on the day/night border (called the terminator). It looks a lot like the Moon, doesn’t it? They’re similar, both being gray from lava-flooded basaltic rock, and craters everywhere. I think the rayed crater on the extreme left is Debussy, but I’m not sure, and it’s not labeled in the press release image (rays are crated when plumes of material shot out from the impact land on the surface). 

Don’t forget, there are two other spectacular images released as well; check the link above for those.

BepiColombo still has two flybys to go (in December 2024 and January 2025). It’ll then be moving much more slowly relative to Mercury, so it’ll take it nearly two more years before it can approach the planet and settle into orbit in November 2026. I can’t wait! It’s a fascinating planet, and close-up images of it will be amazing.

Mercury is obviously a difficult planet to get to because it’s so close to the Sun, but it’s also hard to observe from Earth for the same reason. It’s a morning star right now, and soon will appear over the western horizon after sunset once it rounds behind the Sun. However, it won’t get very high in the sky for northern hemisphere observers (if you’re close to the equator the viewing is better). It won’t be high enough to see easily after sunset until around March of next year, and even then it only gets about 10° above the horizon. I’ve spotted it many times (usually with binoculars) and it’s fun to see it as a faint dot in the gloaming. It’s also cool to know that we’ve sent spacecraft there before, and another that will soon be there.

You can email me at [email protected] (though replies can take a while), and all my social media outlets are gathered together at about.me. Also, if you don’t already, please subscribe to this newsletter! And feel free to tell a friend or nine, too. Thanks!