astronomy

Hell on Earth: NASA’s Toxic Venus Test Chamber

Making a spacecraft to land on Venus (as opposed to orbit it) is really difficult, because the environment on Venus is so extreme. The surface temperature is extremely hot (hot enough to melt lead), the atmospheric pressure is 90 times that on earth, and the atmosphere contains corrosive gases. Because of this, none of the few spacecraft that have successfully landed on Venus so far have been active for more than a few hours.

So NASA is making a Venus environment simulation oven to do testing for possible future missions to Venus, so that they can determine what will or won't last without sending it to the planet and then finding it doesn't work very well.

The chamber could also be used for simulating some other non-Earth environments, such as Jupiter's outer atmosphere.

On an unrelated note, yesterday (at least from my time zone), January 9th, was the anniversary of the death in 1848 of astronomer Caroline Lucretia Herschel. She "found three nebulae and eight comets. In 1787, King George III gave Caroline a salary of 50 pounds per year as assistant to [her brother] William. She published the Index to Flamsteed's Observations of the Fixed Stars and a list of his mistakes in 1797." Caroline's brother William Herschel discovered Uranus.

Three press releases today:
Number one: ESA finds that Venus has an ozone layer too. It was already known that Mars as well as Earth has an ozone layer. They found Venus's by analyzing the spectra of stars seen through the very outer edge of Venus's atmosphere.

Number two: The Secrets of Asteroid Minerva and its Two Moons. Moons let scientists figure out Minerva's mass. They figured out its diameter from a combination of watching it occult a star, and infrared measurements, both of which pointed to a diameter of about 156 km. This lets them calculate its density - about 1.9 grams per cubic centimeter; based on the density of what they think it's made of, that indicates that it must have about 30% empty space in its interior.

Number three: Series of bumps sent Uranus into its sideways spin. This is about a new hypothesis, not a new discovery. The previous standard account for Uranus being tilted on its side was that a single large impact had changed its orientation. The problem with that explanation has always been that it didn't explain why its moons orbit it in similarly tilted orbits. New computer simulation results show that this can be explained if Uranus was hit before the moons formed, while it was still surrounded by a protoplanetary disc out of which the moons later formed, and if it was tilted by two or more impacts, rather than by a single one.

And what I got from Twitter. As before, don't put too much confidence in it; I could very well have misinterpreted things or expanded them wrongly.

Venus
I'm not sure how much of this is new, but: Venus has lightning, and like on Earth, some days have more lightning than others, depending on the weather. The lightning rate on Venus is probably comparable to that on earth, about 100 flashes a second worldwide, but that's hard to prove.

Venus's cloud tops are generally 72 km above the surface, except at the poles where they're only 65 km up.

Global climate models for Earth aren't working for trying to understand Venus, which indicates that they might not be working right for Earth either. To understand Earth's climate, we have to understand Venus too.

Saturn's moons
One of the puzzles about Saturn's moon Iapetus is why it has a ridge running around its equator. One hypothesis has been that it used to be spinning faster, which made it more oblate (i.e., bigger around at the equator than at the poles) due to centrifugal effects, but its rotation slowed, so gravity made it more spherical than oblate, but the rearrangement process from more oblate to less oblate created an equatorial ridge. The problem with that is how exactly the spin change could have worked to create that result. The proposal now presented is that if Iapetus once had a satellite of its own, that might make it possible to reduce Iapetus's spin enough to create the ridge. (I don't know how a satellite would help that, though.)

It was discovered over a year ago that Mimas has a weird Pac-Man-shaped temperature pattern; there's a relatively warm area that looks like a Pac-Man shape on images, and relatively cold area on the leading hemisphere that looks like the inside of Pac-Man's mouth. News: The cold part of the leading hemisphere - the area inside Pac-Man's mouth - is correlated with an area in the leading hemisphere that is dark in UV light. Also, as of September 2011, a similar anomaly seems to have been observed on Tethys. (I think this means both the temperature pattern and the correlation with a UV-dark leading hemisphere area have been observed on Tethys, but I'm not sure about the second half.) There's a hypothesis, which still sounds quite tentative, that it might be caused by being bombarded by electrons, which somehow (not clear from Twitter) increase the thermal inertia of the moon's material. (Also not entirely clear to me whether the electrons are bombarding the warmer area or the colder area.)

The outer irregular satellites of Saturn that Cassini observes are so faint that if you were sitting on Cassini, you couldn't see them with the naked eye.

Other stuff
Almost all near-earth asteroids smaller than 60 metres diameter rotate really fast - in less than 2 hours.

Dust from collisions between irregular satellites of Jupiter might have left 100 metres of dust on Callisto and 20-30 metres of dust on Ganymede.

It sounds as if there was some interesting stuff about Europa, but not that I could contextualize well enough to pick out relevant tweets and expand on their significance as needed.

Good news: Jim Green, the Director of Planetary Science for NASA, says that production of Plutonium-238 will be restarted, so there will be a reliable power source for outer solar system missions.

Twitter sources: