On this day in 1994, the Magellan spacecraft stopped transmitting after four years. It had two primary goals: map the surface and gravitational field of the toxic cloud covered planet. Venus is in many ways like Earth. It is almost exactly the same size and density. They both seem to have a similar internal structures. They are both losing heat at the same rate. Yet, as Carl Sagan put it: earth is like heaven and Venus is like hell.

Venus’ surface pressure is almost a hundred times the surface pressure here on earth. Standing on the surface of Venus would be like being a half mile under the ocean. You know: deadly. But it’s worse than that, because it is also incredibly hot. It is 860°F, which is, you know, hotter than any regular kitchen oven. In fact, it is even hotter than the hottest pizza ovens. Venus is very, very hot. In fact, it is hotter than Mercury at noon, even though Venus only gets 25% as much energy from the sun.

The reason for this is because almost 97% of Venus’ atmosphere is composed of carbon-dioxide. This creates the mother of all greenhouse effects. This fact combines with two other aspects of Venus to create a very constant temperature: almost no axial tilt (just 3° compared to 23.5° for Earth) and almost a circular orbit around the sun (eccentricity of 0.007 compared to 0.017 for the Earth). So day, night, pole, or equator, Venus is just too hot even for cooking pizzas. But the temperature does decrease with altitude. So on top of Maxwell Montes — the highest point on Venus at 7 miles — it is only about 700°F. And you know what that means: great pizza oven temperature! (Fun fact: there may be lead sulfide “snow” on top of Maxwell Montes!)

The Magellan mission made a number of discoveries about Venus. For example, it found that the surface was young. It is covered with volcanic material. It appears to have river-like lava flows. It is also geologically active, but doesn’t seem to have plate tectonics. And there is little evidence of wind erosion. Now this is actually something I know a little bit about. First, Venus rotates very slowly (and in the wrong direction), so not much in the way of Coriolis effect. And there are no temperature gradients, so not much mixing due to that. So the atmosphere is very static.

But in September 1994, NASA announced that it was ending Magellan because its solar arrays were decaying and all the mission objectives had been met. So they put it into a gradually decaying orbit. On 11 October, it was down to roughly 85 miles above the surface of Venus. The atmosphere was thick enough at that height to cause the solar arrays to to heat up to 260°F. Two days later, Magellan went around the far side of Venus, and we never heard back. Most of it burned up, but it is assumed that parts of it crashed landed on the surface. Farewell, Magellan!

Much of this article is taken from, Anniversary Post: Magellan.

On this day in 1604, Kepler’s Supernova was first observed. It wouldn’t be noticed by Johannes Kepler until a week later, but he observed it for a year and published a book about it. It’s an important event because it was the last time a supernova was observed in our galaxy. (We observe them in other galaxies.) And that’s really interesting if you consider that just 32 years earlier, Kepler’s colleague Tycho Brahe had observed another supernova. So two supernovas in a small span of time, and then nothing for over 400 years. But that’s the way random events are.

In general, a supernova would have to be closer than 100 light-years from the Earth to have an effect on us. Statistically, we should have one within 33 light-years every 250 million years. That’s one of the things about us being out here on the edge of the galaxy: it’s kind of boring. But it is probably also necessary for the development of advanced life. Further in, life on the Earth would have likely been destroyed before it got too far.

Kepler’s Supernova is thought to have been something on the order of 20,000 light years away. The one Brahe observed was less than half that distance. Still, these supernovas were far, far away — where they belong.

On this day in 1959, the Soviet Luna 3 spacecraft transmitted the first ever pictures of the far side of the Moon. I thought we might take this opportunity to discuss why it is that the same side of the Moon is always facing us. Although I should tell you that this is not exactly true. I think we are able to see about 55% of the Moon’s surface, because it jiggles. But for all intents and purposes, we see the same moon each night. This is because it is tidally locked.

The Moon once rotated rapidly. But over time, the Earth’s gravitational field slowed it. The force from the Earth produces a bulge in the part of the moon that is directly facing the Earth — and also directly opposite (just like the Moon created tides on Earth). This has the effect of squishing down the sides, so that the moon looks like a football with the pointy end facing Earth. Of course, the deformation isn’t anywhere near that great. But that’s the basic idea.

While the Moon was spinning fast, the bulge was always slightly after the direct line. As a result, the gravitational field had a net torque on the Moon, slowing its rotation. The effect was very small. But it’s amazing what you can accomplish in a billion years. I used to tell my students to image the Moon (or any other tidally locked object like Mercury) as if it were a frying plan. The handle would always be facing just a little off center from the Earth, and would thus be constantly pulled slightly in the opposite direction of the Moon’s rotation.

Luna 3 was the first mission specifically meant to photograph the other side of the Moon. Luna 1, sent in January of that year, was meant to crash on the Moon. It missed. (Don’t laugh: we missed the Moon the first time we tried.) And it became the first human object to go into orbit around the Sun. Luna 2, sent in September, actually hit the Moon. Later, in February 1966, Luna 9 would be the first spacecraft to make a soft landing on the Moon (or any other place).

The radio signal on Luna 3 was so weak, that the spacecraft had to get almost all the way back to Earth in order to transmit its 18 images. The one above is the first transmitted back. I think we humans have become far too cavalier about this kind of stuff. What we now do in space is mind boggling. It’s always nice to go back five or six decades and see what we were doing and just how hard it was. Oh, and no one knows for sure what happened to Luna 3. But it probably burned up in the Earth’s atmosphere.

On this day in 1995 — 20 years ago — Bellerophon (51 Pegasi b) was discovered. It was the first planet discovered to be orbiting around a Sun like star — 51 Pegasi. It was the second exoplanet ever discovered. And it is quite a planet, which destroyed some theories about solar system formation. It is a very big planet: roughly half the mass of Jupiter. But it is really close to 51 Pegasi — just 0.05 AU, which is six times closer than Mercury is to the Sun. The year on Bellerophon is four Earth days long.

Bellerophon was discovered the way that about half of all exoplanets have been discovered: with Doppler spectroscopy. I put the animation above (courtesy of Zhatt at Wikipedia) so that you would see how this works. As I’ve discussed before, Jupiter doesn’t actually orbit around the Sun; it orbits around the center of mass of it and the Sun (forget the rest of the solar system for now). But as a result, the Sun also orbits around the center of mass of the solar system.

As a result of Jupiter, the Sun wobbles — changing speed by about 12 m/s over the course of one Jupiter orbit (12 years). Since the 1990s, we’ve had equipment capable of detecting Jupiter if we were observing from another solar system. In the case of 51 Pegasi, the wobble was much greater: 70 m/s. But in the early 2000s, new systems were installed that could detect wobbles as small as 0.3 m/s. And soon, we should have systems that can detect wobbles of just 0.1 m/s. That last one is important because the Earth induces a 0.1 m/s wobble in the Sun. It’s very exciting.