I recently talked about some of the most habitable exoplanets which unfortunately we’ll never be able to reach because our technology can’t do it. But there are some very interesting concepts being developed that could change all that – if they work.
Precise measurements of Cassini’s final trajectory have now allowed scientists to make the first accurate estimate of the amount of material in the planet’s rings, weighing them based on the strength of their gravitational pull.
That estimate about 40 percent of the mass of Saturn’s moon Mimas, which itself is 2,000 times smaller than Earth’s moon tells them that the rings are relatively recent, having originated less than 100 million years ago and perhaps as recently as 10 million years ago.
Their young age puts to rest a long-running argument among planetary scientists.
Some thought that the rings formed along with the planet 4.5 billion years ago from icy debris remaining in orbit after the formation of the solar system.
Others thought the rings were very young and that Saturn had, at some point, captured an object from the Kuiper belt or a comet and gradually reduced it to orbiting rubble.
The new mass estimate is based on a measurement of how much the flight path of Cassini was deflected by the gravity of the rings when the spacecraft flew between the planet and the rings on its final set of orbits in September 2017.
Initially, however, the deflection did not match predictions based on models of the planet and rings.
Only when the team accounted for very deep flowing winds in atmosphere on Saturn, something impossible to observe from space, did the measurements make sense, allowing them to calculate the mass of the rings.
They also calculated that the surface clouds at Saturn’s equator rotate 4 percent faster than the layer 9,000 kilometers (about 6,000 miles) deep.
That deeper layer takes 9 minutes longer to rotate than do the cloud tops at the equator, which go around the planet once every 10 hours, 33 minutes.
Militzer also was able to calculate that the rocky core of the planet must be between 15 and 18 times the mass of Earth, which is similar to earlier estimates.
The team, led by Luciano Iess at the Sapienza University of Rome, Italy, reported their results today in the journal Science.
It turns out that Uranus is so weird because of a massive collision billions of years ago.
A new study confirms that this collision with a huge object — which was approximately twice the size of Earth — could have led to the planet’s extreme tilt and other odd attributes.
Uranus, the planet with the unforgettable name, is unique in a number of ways.
“All of the planets in the solar system are spinning more or less in the same way … yet Uranus is completely on its side,” Jacob Kegerreis, the new study’s lead author and a researcher at Durham University’s Institute for Computational Cosmology in the U.K. said.
And this isn’t the only thing that makes the planet so strange.
Uranus also has a “very, very strange” magnetic field and is extremely cold, even though it “should” be warmer, according to Kegerreis.
In this study, Kegerreis and his team of astronomers seek to explain many of the planet’s odd features by attributing them to a collision with a massive, icy object about 4 billion years ago.
To better understand how the impact affected Uranus’ evolution, the team used a high-powered supercomputer to run a simulation of massive collisions — something that has never been done before.
This study confirms an older study that suggested Uranus’ significant tilt was caused by a collision with a massive object.
The researchers suspect that this object was probably a young protoplanet, made up of rock and ice. This collision is “pretty much the only way” that we can explain Uranus’ tilt, Kegerreis said.
Amazingly, Uranus retained its atmosphere after this impact.
The researchers think that this is because the object only grazed the planet, hitting it hard enough to change its tilt but not enough to affect its atmosphere, according to a statement from Durham University.
It’s likely that this type of event isn’t uncommon in the universe: “All the evidence points to giant impacts being frequent during planet formation, and with this kind of research, we are now gaining more insight into their effect on potentially habitable exoplanets,” Luis Teodoro, study co-author and researcher at the BAER/NASA Ames Research Center, said in the statement.
But this enormous object crashing into Uranus did more than just knock it into a new tilt.
According to this research, when the object hit Uranus, some of the debris from the impact may have formed a thin shell that continues to trap heat coming from the planet’s core.
This could at least partially explain why Uranus’ outer atmosphere is extremely cold.
According to Kegerreis, this collision could also explain two other oddities about the tilted planet. First, it could explain how and why some of Uranus’ moons formed.
The researchers think that the impact could have knocked rock and ice into the young planet’s orbit — debris that later became some of Uranus’ 27 moons.
Additionally, they think that the collision could have altered the rotation of any moons that already existed at the time. Last year, a separate study also explored this aspect of the collision.
The researchers also suggest that the collision could have created molten ice and lumps of rock inside the planet, which tilted its magnetic field, according to the statement.
Following this study, the researchers hope to study this collision with even higher-resolution simulations to better understand Uranus’ evolution, according to Kegerreis.
He also noted that the team aims to study Uranus’ chemistry and the different ways that an impact like this could have affected its atmosphere.
The weird linear grooves scoring the surface of the Mars moon Phobos were likely carved by boulders knocked loose by a giant impact, a new study suggests.
That impact created Phobos’ most notable feature — the 5.6-mile-wide (9 kilometers) Stickney Crater, which is about one-third as wide as the moon itself.
“These grooves are a distinctive feature of Phobos, and how they formed has been debated by planetary scientists for 40 years,” study lead author Ken Ramsley, a planetary scientist at Brown University in Providence, Rhode Island, said in a statement.
“We think this study is another step toward zeroing in on an explanation.”
Mars has two tiny moons — Phobos and Deimos, both of which the Red Planet may have nabbed from the nearby asteroid belt long ago.
Phobos’ parallel grooves were first spotted in the 1970s by NASA’s Mariner and Viking missions. In the decades since, researchers have advanced many hypotheses to explain their origin.
For example, they may have been carved by material blasted off Mars by powerful impacts. Or they could be strain marks showing that Mars’ gravity is tearing Phobos apart.
Or bouncing, rolling boulders freed by the Stickney-causing impact could have created the grooves. This idea was first advanced in the late 1970s by researchers Lionel Wilson and Jim Head, the latter of whom is a co-author on the new study.
In the new work, the researchers used computer models to simulate how debris set in motion by the Stickney smashup may have traveled across Phobos’ surface.
“The model is really just an experiment we run on a laptop,” Ramsley said in the same statement. “We put all the basic ingredients in, then we press the button and we see what happens.”
What happened supports the rolling-boulder idea, study team members said. In the simulations, for example, rocks set in motion by the Stickney impact tended to travel on parallel paths, matching the observed groove patterns.
In addition, some of the simulated boulders traveled all the way around Phobos, rolling over the tracks of their fellow bounders. This could explain an oddity of the actual grooves — that some of them overlay one another.
There’s another puzzling aspect of the Phobos features — a weird “dead spot” free of grooves. But the new modeling work has an answer for that, too: The dead spot is a low-elevation area just beyond a slight “lip” of rock.
“It’s like a ski jump,” Ramsley said. “The boulders keep going, but suddenly there’s no ground under them. They end up doing this suborbital flight over this zone.”
All in all, the work “makes a pretty strong case” that the “rolling-boulder model accounts for most if not all the grooves on Phobos,” Ramsley said.
The eight planets in our solar system differ in lots of ways. They are different sizes. They are different distances from the sun. Some are small and rocky, and others are big and gassy.
But they’re all nice and round. Why is that? Why aren’t they shaped like cubes, pyramids, or discs?
Planets form when material in space starts to bump and clump together. After a while it has enough stuff to have a good amount of gravity.
That’s the force that holds stuff together in space. When a forming planet is big enough, it starts to clear its path around the star it orbits. It uses its gravity to snag bits of space stuff.
A planet’s gravity pulls equally from all sides. Gravity pulls from the center to the edges like the spokes of a bicycle wheel. This makes the overall shape of a planet a sphere, which is a three-dimensional circle.
Are they all perfect, though?
While all the planets in our solar system are nice and round, some are rounder than others. Mercury and Venus are the roundest of all. They are nearly perfect spheres, like marbles.
But some planets aren’t quite so perfectly round. Saturn and Jupiter are bit thicker in the middle. As they spin around, they bulge out along the equator. Why does that happen?
When something spins, like a planet as it rotates, things on the outer edge have to move faster than things on the inside to keep up.
This is true for anything that spins, like a wheel, a DVD, or a fan. Things along the edge have to travel the farthest and fastest.
Along the equator of a planet, a circle half way between the north and south poles, gravity is holding the edges in but, as it spins, stuff wants to spin out like mud flying off a tire.
Saturn and Jupiter are really big and spinning really fast but gravity still manages to hold them together. That’s why they bulge in the middle. We call the extra width the equatorial bulge.
Saturn bulges the most of all the planets in our solar system. If you compare the diameter from pole to pole to the diameter along the equator, it’s not the same.
Saturn is 10.7% thicker around the middle. Jupiter is 6.9% thicker around the middle. Instead of being perfectly round like marbles, they are like basketballs squished down while someone sits on them.
What about the other planets?
Earth and Mars are small and don’t spin around as fast as the gas giants. They aren’t perfect spheres, but they are rounder than Saturn and Jupiter.
Earth is 0.3% thicker in the middle, and Mars is 0.6% thicker in the middle. Since they’re not even one whole percentage point thicker in the middle, it’s safe to say they’re very round.
As for Uranus and Neptune, they’re in between. Uranus is 2.3% thicker in the middle. Neptune is 1.7% thicker. They’re not perfectly round, but they’re pretty close.
The most prolific planet-hunting machine in history has signed off.
NASA’s Kepler space telescope, which has discovered 70 percent of the 3,800 confirmed alien worlds to date, has run out of fuel, agency officials announced last October 30.
Kepler can no longer reorient itself to study cosmic objects or beam its data home to Earth, so the legendary instrument’s in-space work is done after nearly a decade.
And that work has been transformative.
“Kepler has taught us that planets are ubiquitous and incredibly diverse,” Kepler project scientist Jessie Dotson, who’s based at NASA’s Ames Research Center in Moffett Field, California said.
“It’s changed how we look at the night sky.”
The announcement was not unexpected. Kepler has been running low on fuel for months, and mission managers put the spacecraft to sleep several times recently to extend its operational life as much as possible.
But the end couldn’t be forestalled forever; Kepler’s tank finally went dry two weeks ago, mission team members said during a telecon with reporters today.
“This marks the end of spacecraft operations for Kepler, and the end of the collection of science data,” Paul Hertz, head of NASA’s Astrophysics Division, said during the telecon.
Not done yet
Even though Kepler has closed its eyes, discoveries from the mission should keep rolling in for years to come.
About 2,900 “candidate” exoplanets detected by the spacecraft still need to be vetted, and most of those should end up being the real deal, Kepler team members have said.
A lot of other data still needs to be analyzed as well, Dotson stressed.
And Kepler will continue to live on in the exoplanet revolution it helped spark.
For example, in April, NASA launched a new spacecraft called the Transiting Exoplanet Survey Satellite (TESS), which is hunting for alien worlds circling stars that lie relatively close to the sun (using the transit method, just like Kepler).
Kepler’s death “is not the end of an era,” Kepler system engineer Charlie Sobeck, also of NASA Ames said. “It’s an occasion to mark, but it’s not an end.”