Jupiter is Stranger Than We Thought

On the one hand, it's hardly surprising that an enormous gas giant doesn't work the way we first thought it did. It's space. Conventional logic is usually wrong. On the other hand, it's still surprising. It's not like Jupiter is a complete unknown to us, with Galileo fulfilling the same role Cassini is currently (though not for much longer) performing around Saturn. It was a big flagship space probe that orbited Jupiter for nearly 8 years, and in doing so vastly expanded our knowledge of Jupiter and the Jovian system.

(Brief aside: Cassini and Galileo may be very similar space probes, but I don't think there's a question that Cassini was by far the more successful of the two. Galileo suffered several technical issues that hindered its abilities and orbited for 8 years, whereas Cassini has suffered no such problems and has orbited for 13 years.)

It's been nearly 14 years since Galileo took its final dive into Jupiter, and once again, a space probe orbits Jupiter. Juno is a space probe designed to learn more about Jupiter itself rather than its moons, and from polar orbit it has done a very good job of this. For one thing, the Jovian polar regions don't match the rest of the planet. You think of Jupiter, you see the red, brown, and white stripes, but in fact, the poles are mostly blue. And that's just an obvious thing we learned because we finally got a chance to look at Jupiter's poles (Jupiter has almost no tilt, so it was impossible to get an image of them without sending a probe into polar orbit).

Suffice to say, a gas giant that bears almost no resemblance to Earth has an atmosphere that operates in ways entirely different to our own. For one, the enormous Jovian auroras work in reverse, caused by electrons leaving the polar regions, rather than entering them as they do on Earth. It also appears that the sun is not the primary driver of weather on Jupiter, and once you drop below the upper atmosphere, things don't quiet down. The lower parts of the atmosphere are just as diverse as the upper parts. A big band of ammonia orbiting the equator was particularly interesting, as there is no good reason why it should be there at all.

Things don't get quieter even further down in Jupiter's central regions. There are noticeable fluctuations in Jupiter's gravitational and magnetic fields, indicating a non-uniform interior and deep convection within the planet. The article concludes with a quote that I find rather appropriate, both to this current situation and to astronomical science in general: "In hindsight, it’s hard to imagine why would we have ever thought it would be simple and boring." Indeed.

Something on Venus is Colder Than Expected

That's not a phrase often used when talking about the second planet from the Sun. "Colder Than Expected". This is Venus we're talking about, the planet where the rain is sulfuric acid, and the surface temperature sits at a rather toasty 900 degrees Fahrenheit. But that's the news we've gotten from the no-longer-with-us Venus Express, whose mission officially ended in December 2014. Hey, it takes a while to get through all the data.

In 2014, the probe ran out of fuel, and as it slowly fell towards Venus, its orbits actually took it through the upper portion of the upper Venusian atmosphere, specifically at the poles. While the probe was down there, the people in charge decided to do some science. The probe found that the upper atmosphere was sitting around -250 degrees Fahrenheit, significantly colder than what was expected. They also found that at heights of 130 and 140 kilometers, atmospheric pressure was 22% and 40% less than expected.

So why is this occurring? Scientists believe it has something to do with the presence of Venus' strong polar vortices, along with strong atmospheric gravity waves.

The scientists also note that the Venus Express trip through the Venusian atmosphere will be useful for the ExoMars probe, which will be undergoing aerobraking when it arrives at Mars.

Pluto: The Saga Continues

Yes, it's time for another installment of big Pluto news. New Horizons is still sending back data, and will be for several months. As that data comes in, we learn more and more about this surprisingly complex little world. A group of five studies was recently published in the journal Science about Pluto, so let's take a look at what scientists have learned.

The first piece of news is that Pluto's surface has a lot of variation in which type of ice is dominant. There are areas which are mostly methane ice, areas which are mostly nitrogen ice, and areas which are mostly water ice. Nitrogen ice is dominant in the flat, craterless plains, while water ice is dominant in the mountainous regions, reflecting their characteristics at the very cold temperature Pluto sits at. Water ice is very rigid and behaves almost like rock does on Earth, while nitrogen ice is much less tough and is able to flow, much like our glaciers on Earth. Indeed, this sort of distinct differentiation in material most closely resembles Earth, where the surface is separated by areas dominated by water and by rock.

Another study focuses on the geology of Pluto, especially Sputnik Planum, the vast, nitrogen ice dominated region in the southern hemisphere. The plain is located on an ancient impact crater, and its smooth, craterless surface contrasts sharply to areas with a heavy crater density scientists were likely expecting all over Pluto, and to areas with an intermediate crater density. Small bodies like Pluto should have frozen solid all the way through billions of years ago, but something is causing Sputnik Planum and much of the surface to refresh itself, though what that mechanism is remains unknown. The same study also demonstrates that Cthulhu Regio is covered in tholins, an organic molecule that has turned the area a deep red. The tholins likely drifted down from the atmosphere and the mountains Wright Mons and Piccard Mons. These are big mountains, Wright Mons is 2.5 miles high and Piccard Mons is 3.7 miles high, and likely formed through cryovolcanism.

Pluto's atmosphere was the focus of a third study. It's a bit less interesting, but it turns out that the Plutonian atmosphere is significantly colder than what was predicted before New Horizons' visit. Because of this, the particles of the upper atmosphere are much less energetic, which in turn means the atmosphere is losing gas at a much slower rate than what was anticipated. Initial estimates were off by about a factor of 5,000.

Don't worry, Pluto's five moons weren't forgotten in all this new research. Pluto's biggest moon Charon is actually quite a bit different from Pluto, and closer in line to what scientists were expecting. There is some very dramatic topography, but on the whole, Charon is a dead world, and has been for about 4 billion years. Its surface is mostly water ice, and is lacking significant amounts of methane and nitrogen ice like Pluto has. Why this is the case is unclear. An additional study examined the 4 smaller moons, which are much more reflective than more typical Kuiper Belt objects, and move very chaotically. This bolsters the theory that the moons are bits of debris that were thrown off in an enormous collision early on in Pluto's history, and the 4 moons are survivors that have managed to escape being sucked up by either Pluto or Charon.

Credit: NASA/John Hopkins University Applied Physics
 Laboratory/Southwest Research Institute

In news unrelated to the Science studies, scientists recently announced that as recently as 800,000 years ago, Pluto likely had a much thicker atmosphere, more substantial than even Mars. Right now, the Plutonian atmosphere has a pressure about 1/100,000 that of Earth's, and this is likely what it usually is. However, Pluto has a axial tilt of about 120 degrees, and as the planet's tilt slowly undergoes procession, there are certain times when the amount of solar radiation in areas with lots of volatile ices goes up dramatically. The resulting outgassing would thicken the atmosphere so that the pressure would increase to about a tenth of Earth's. This is significantly thicker than the Martian atmosphere, and potentially thick enough to allow liquid nitrogen to flow freely on the surface. A thicker atmosphere with liquid nitrogen streams and ponds would explain a series of unusual surface features, such as empty channels similar to those seen on Mars, and a flat, icy area that resembles a frozen pond. The possibility of a thick atmosphere and the existence of a nitrogen cycle similar to Earth's water cycle, even if temporary and limited, on such a tiny, cold world seems pretty far-fetched, but ever since New Horizons flew by, Pluto has surprised us. This batch of new science has made Pluto that much more interesting.

It's still not a planet though.

Terraforming Mars Just Got a Lot Harder

The act of terraforming a planet, even one as comparatively hospitable as Mars, would never be an easy task. But whenever discussing mankind's future on the Red Planet, it seemed to be the inevitable conclusion. We would colonize Mars, and then change it in Earth's image. It would be a daunting task of engineering, and the ethical dilemma of uprooting any potential native life was not going to go away either, but it almost seemed a foregone conclusion that we would eventually terraform Mars.

Mars is probably going to stay red in the future.

According to data from the MAVEN space probe currently orbiting Mars and studying the Martian atmosphere, however, there may be a big problem with future terraforming endeavors. The infant Mars had a thick atmosphere, but as time went on, that atmosphere was lost. It was assumed that most of the carbon dioxide that originally made up the atmosphere had frozen out into the soil, but that is not the case. Once Mars lost its magnetic field, the solar wind, more active when the Sun was young, pummeled the planet, and Mars, already much smaller and with much weaker gravity than Earth, had no way to hold onto its atmosphere. It took maybe around 500 million years, and by around 3.7 billion years ago, the Mars we know today had taken shape. 

Why is this bad for terraforming? Well, if the carbon dioxide had settled into the Martian soil, warming the planet back up again would release it, building up the atmosphere and setting up a greenhouse effect (a good thing in this case), which would heat the planet up even more, releasing even more carbon dioxide and so on. But the carbon dioxide from the original Martian atmosphere is just gone, lost forever to the cosmos. There is still some on the surface, frozen in the ice caps, but likely not enough to work with. This news does not necessarily mean Mars cannot be terraformed, but in order to do so, it's going to take more than just warming the place up.