Enlarge / InSight captured seismic waves released when an impact formed this crater in 2021. But a similar event can't be tied to any craters.

Earth has earthquakes. Mars has marsquakes . There is just one difference: marsquakes are most frequently caused by meteoroid crashes since the Red Planet lacks the tectonic plates that shift pieces of crust on Earth. So what caused the most intense marsquake ever when there has been no evidence of a collision?

Vibrations from the 4.7 magnitude quake sent tremors through the Martian crust for six hours (if not more) and were captured by NASA’s InSight lander in May 2022. Otherwise known as S1222a, this marsquake was assumed to have been caused by a meteoroid impact , so an international team of researchers immediately began searching for evidence of a fresh crater. The problem was that none existed. That's when the team, led by planetary geophysicist Benjamin Fernando, began thinking that something was potentially going on beneath the surface.

“We undertook a comprehensive search of the region in which the marsquake occurred,” Fernando and his team said in a study recently published in Geophysical Research Letters . “We did not identify any fresh craters in the area, implying that the marsquake was likely caused by geological processes.”

Enlarge / Modeling has shown how material ejected from the Earth by a massive collision could have formed the Moon. Now the models are being used to look at what happened inside the Earth. (credit: NASA )

Seismic waves created by earthquakes as they travel through the planet's interior change speed and direction as they move through different materials. Things like rock type, density, and temperature all alter the travel of these waves, allowing scientists to gradually build up a picture of the Earth's crust and mantle, spotting things like the rise of plumes of hot mantle material, as well as the colder remains of tectonic plates that dropped off the surface of the Earth long ago.

There are some things that show up in these images, however, that aren't easy to explain. Deep in the Earth's mantle there are two regions where seismic waves slow down, termed large low-velocity provinces. This slowdown is consistent with the materials being higher density, so it's not really a surprise that they're sitting near the core. But that doesn't explain why there are two distinct regions of them or why they appear to contain material that has been there since the formation of the Solar System.

Now, a team of scientists has tied the two regions' existence back to a catastrophic event that happened early in our Solar System's history: a giant collision with a Mars-sized planet that ultimately created our Moon.

Enlarge / Image showing a dust storm over the northern hemisphere of Mars. (credit: ISRO)

If the explorers from Journey to the Center of the Earth were to journey to the center of Mars instead, they definitely wouldn’t come across the subterranean oceans or live dinosaurs they encountered in the movie, but they would probably see something different from our planet’s core.

Earth has a mantle of rock that moves like a sluggish liquid. Beneath the mantle is a liquid iron outer core and solid iron inner core. Because Earth and Mars are both rocky planets, and might have even had similar surface conditions billions of years ago, does that mean we should expect the same interior on Mars? Not exactly.

When two teams of researchers used data from NASA’s InSight lander and other spacecraft to get as close to the core of Mars as they could in a lab, they found that the red planet is not much like Earth on the inside. Data from NASA’s InSight lander’s SEIS (Seismic Experiment for Interior Structure) project had previously suggested that Mars has a large core that is not very dense. But the new analysis, which included additional seismic signals, indicates that what was once thought to be the surface of the Martian core is actually a thick molten rock layer. The actual core of Mars is most likely much smaller.

Enlarge / Computer-generated conception of the hot, metal planet. (credit: NASA )

Metals are everywhere in the Universe, from hot gas giants where it rains molten iron to heavy elements formed as a star goes supernova. Exoplanet GJ 367b one-ups them all. This planet is made of metal.

GJ 367b is an extreme planet. This “super Mercury,” which orbits its star once every 7.7 hours, was first discovered by NASA’s TESS planet hunter in 2015. Now, scientists from the University of Turin in Italy and the Thüringer Landessternwarte in Germany have examined more recent measurements of the planet using ESO’s HARPS spectrograph along with the original TESS observations. They found that this object is almost twice as dense as Earth—which suggests it is most likely made of solid iron.

Even though GJ 367b is now a solid iron planet, it might have once been the core of an ancient rocky planet.

Enlarge / Some of the ice near the South Pole of Mars stays around all year long. (credit: NASA/JPL-Caltech/Univ. of Arizona )

Mars is a vast, frozen desert. Nowhere is that more evident than at its poles, which are the coldest regions on the planet. However, it looks like the weather forecast for its harsh winters and slightly more forgiving springs could be different from we thought.

Like Earth, Mars has a volatile cycle that sees snow and ice levels fluctuate as temperatures plummet in the winter and start to rise again in the spring. Unlike Earth, Martian snowfall includes CO ₂ snow and is influenced by different phenomena. Now, a team of researchers led by Haifeng Xiao of Berlin Technical University in Germany is reexamining the change in snowfall over the course of a year at the Martian north pole. Their findings suggest that forces such as sublimation might mean there is more snow in the winter—and less in the spring—than previously thought.

“We propose to use the shadow variations [of ice blocks] to infer the seasonal depths at high polar latitudes,” Xiao and his team said in a draft manuscript recently published in the Earth and Space Science Open Archive.

Enlarge / In addition to craters, Mercury's terrain features faults generated by the planet's cooling. (credit: NASA )

The planet Mercury may be hot, but it appears to be cooling down. That's the conclusion of a new study that looked for the kinds of features on Mercury that can form as the surfaces of planets contract due to cooling. These vertical faults, called "graben," are not only common across the planet's surface but appear to have formed within the last few hundred million years—and possibly much more recently.

All of which suggests that the stresses caused by a cooling planet are still playing out on the Solar System's smallest non-dwarf planet.

Crunch time

The process of building a planet necessarily generates a lot of heat as impactors of various sizes deliver both matter and energy to the growing planet. The radioactive elements they deliver can also heat the planet's interior. For the rocky planets of our Solar System, this heat means a differentiated interior, with layers of lighter rocks on top of a liquid core.

Enlarge / Scientists created this mosaic of asteroid Bennu using imagery collected by NASA's OSIRIS-REx spacecraft. The asteroid spans about 1,600 feet (500 meters) across.

A NASA spacecraft will complete a round-trip journey to an asteroid this weekend, returning to Earth after a seven-year voyage to bring back unspoiled rock specimens from an alien world that could yield insights into the formation of life.

The landing Sunday at 8:55 am local time in Utah (10:55 am EDT or 14:55 UTC) will wrap up a round-trip journey of 4.4 billion miles (7.1 billion kilometers) for NASA's robotic OSIRIS-REx mission. The return will set into motion another sequence of tightly-choreographed events to secure the asteroid sample capsule, fly it halfway across the country to a NASA facility at the Johnson Space Center in Houston, then open it up to reveal the bounty inside.

"The spacecraft trajectory and performance have just been spot on," said Sandra Freund, OSIRIS-REx's program manager at Lockheed Martin, which built and operates the spacecraft on behalf of NASA. "We have just a few remaining steps before we have Bennu samples on the ground."

Enlarge / A self portrait of InSight's hardware on the red planet. (credit: NASA/JPL-Caltech)

To say Mars is a bizarre planet might be something of an understatement. It has nearly no atmosphere, has an unstable liquid metal core that causes it to wobble on its axis constantly, and as a frozen desert, is an oxymoron in itself. As if Mars wasn’t strange enough, data from NASA’s InSight Lander (RIP) has now revealed that the red planet is spinning faster and faster every year.

The increasing spin went unknown until a research team found evidence of acceleration through InSight’s RISE (Rotation and Interior Structure Experiment) instrument. That same team, led by radio scientist Sebastien Le Maistre of the Royal Observatory of Belgium, who is also the principal investigator of RISE, had previously found that the core of Mars is most likely a glob of molten metal. Looking further into RISE data from InSight’s first 900 days on Mars, they saw that the planet’s spin was accelerating by a fraction of a millisecond per (Earth) year, or about 0.76 milliseconds. Martian days are gradually growing shorter. But why?

What lies beneath—or above

RISE’s main objective was to see how much Mars wobbled as its orbit was pushed and pulled by the gravity of the Sun. This would determine whether the core was more likely to be solid or liquid. However, RISE also had another task, which was measuring the length of a Martian day. Days on Mars, known as sols, are about a half-hour longer than Earth days at 24 hours and 37 minutes. RISE measured both the rotation rate and wobbling of Mars with reflected radio waves. When it received a radio signal from NASA’s Deep Space Network (DSN), it would reflect those waves right back at Earth. The difference between the frequency of the signal sent out by the DSN and the signal that bounced back to Earth told the InSight team how the lander was moving along with Mars.

Enlarge / The newly described deposits (left) have their shapes highlighted in red at right. (credit: NASA/JPL-Caltech/MSSS/IRAP )

The prodigious evidence for water on Mars has eliminated scientific debate about whether Mars had a watery past. It clearly did. But it has left us with an awkward question: What exactly did that past look like? Some results argue that there were long-lived oceans and lakes on Mars. Others argue that the water largely consisted of ice-covered bodies that only allowed water to burst out onto the surface on occasions .

The picture is further confused by the fact that some or all of these may have been true at different times or in different locations. Creating a clear picture would help shape our understanding of an environment that might have been far more conducive to life than anything that exists on present-day Mars.

A new paper describes evidence that at least one part of Mars went through many wet/dry cycles, which may be critical for the natural production of molecules essential to life on Earth—though they don't necessarily mean conditions in which life itself could thrive.