Jupiter's moon Ganymede is the largest moon in the Solar System and may have an ocean sandwiched between two layers of ice. But how warm is that ocean? Image Credit: By National Oceanic and Atmospheric Administration Public Domain, https://commons.wikimedia.org/w/index.php?curid=8070396
Ganymede’s surface is a bit of a puzzle for planetary scientists. About two-thirds of its surface is covered in lighter terrain, while the remainder is darker. Both types of terrain are ancient, with the lighter portion being slightly younger. The two types of terrain are spread around the moon, and the darker terrain contains concurrent furrows.
For the most part, scientists think that the furrows were caused by tectonic activity, possibly related to tidal heating as the moon went through unstable orbital resonances in the past.
But a new study says that a massive impact might be responsible for all those furrows.
This artist’s concept shows a hypothetical planet covered in water around the binary star system of Kepler-35A and B. The composition of such water worlds has fascinated astronomers and astrophysicists for years. (Image by NASA/JPL-Caltech.)
We all know what water is. And what rock is. The difference is crystal clear. Well, here on Earth it is.
But on other worlds? The difference might not be so clear.
We intend to explore the Moon, use its resources, and use it as a jumping-off point for missions deeper into the Solar System. For that we need a Lunar GPS. Image Credit: NASA
The Moon is easily the most well-studied object in the Solar System, (other than Earth, of course.) But it still holds some puzzles for scientists. Why, for instance, is one side of the Moon so different from the other?
Impactors strike during the reign of the dinosaurs (image credit: MasPix/devianart)
There are bad days, and then there are really bad days. 65 million years ago, life on Earth – especially if you were a dinosaur – experienced the worst possible bad day, as a giant meteor came crashing down to the surface of our planet, unleashing an inferno followed by decades of nuclear winter. And the worst part? It didn’t have to be so bad.
A geological map of the Moon showing different formations and mineral deposits. Credit: NASA/GSFC/USGS
The prospect of mining asteroids and the Moon is on a lot of peoples’ minds lately. Maybe it’s all the growth that’s happened in the commercial aerospace industry in the past few decades. Or perhaps it’s because of Trump’s recent executive order to allow for asteroid and lunar mining. Either way, there is no shortage of entrepreneurs and futurists who can’t wait to start prospecting and harvest the natural bounty of space!
Coincidentally enough, future lunar miners now have a complete map of the lunar surface, which was created by the US Geological Society’s (USGS) Astrogeology Science Center, in collaboration with NASA and the Lunar Planetary Institute (LPI). This map shows the distribution and classification of the mineral deposits on the Moon’s surface, effectively letting us know what its familiar patchwork of light and dark patches the really are.
Artist's depiction of a waterworld. A new study suggests that Earth is in a minority when it comes to planets, and that most habitable planets may be greater than 90% ocean. Credit: David A. Aguilar (CfA)
Evidence from an ancient section of the Earth’s crust suggest that Earth was once a water-world, some three billion years ago. If true, it’ll mean scientists need to reconsider some thinking around exoplanets and habitability. They’ll also need to reconsider their understanding of how life began on our planet.
An artist's illustration of the Ordovician Meteor Event. Image Credit: DON DAVIS, SOUTHWEST RESEARCH INSTITUTE
About 466 million years ago, there was an asteroid collision in the asteroid belt between Mars and Jupiter. The collision caused the breakup of a major asteroid, creating a shower of dust throughout the inner Solar System. That event is called the Ordovician Meteor Event, and its dust caused an ice age here on Earth.
That ice age contributed to an enormous boost in biodiversity on ancient Earth.
It is believed that 4.4 billion years ago, a celestial body (Theia) slammed into Earth and produced the Moon. Image Credit: NASA/JPL-Caltech
The most comprehensive and widely-held theory of how the Moon formed is called the ‘giant impact hypothesis.’ That hypothesis shows that about 150 million years after the Solar System formed, a roughly Mars-sized planet named Theia collided with Earth. Though the timeline is hotly-debated in the scientific community, we know that this collision melted Theia and some of Earth, and that molten rock orbited around Earth until it coalesced into the Moon.
But now a new study, though not contradicting the giant impact hypothesis, is suggesting a different timeline, and an older Moon.
People always want to know how old everything is. And more specifically, they want to know how we know how old everything is. Well, here at Astronomy Cast, it’s our job to tell you now only what we know, but how we know what we know. And today we’ll begin a series on how we know how old everything is.
A 13-kilometer (8-mile) diameter crater being infilled by the Medusae Fossae Formation. Credit: High Resolution Stereo Camera/European Space Agency.
Scientists first observed the Medusae Fossae Formation (MFF) in the 1960s, thanks to the efforts of the Mariner spacecraft. This massive deposit of soft, sedimentary rock extends for roughly 1,000 km (621 mi) along the equator and consists of undulating hills, abrupt mesas, and curious ridges (aka. yardangs) that appear to be the result of wind erosion. What’s more, an unusual bump on top of this formation also gave rise to a UFO conspiracy theory.
Needless to say, the formation has been a source of scientific curiosity, with many geologists attempting to explain how it could have formed. According to a new study from Johns Hopkins University, the region was the result of volcanic activity that took place on the Red Planet more than 3 billion years ago. These findings could have drastic implications for scientists’ understanding of Mars’ interior and even its past potential for habitability.
Perspective view of Medusa Fossae looking south-east. Copyright: ESA/DLR/FU Berlin (G. Neukum)
Ojha’s past work includes finding evidence that water on Mars occurs in seasonal brine flows on the surface, which he discovered in 2010 as an undergraduate student. Lewis, meanwhile, has dedicated much of his academic carreer to the in-depth study of the nature of sedimentary rock on Mars for the sake of determining what this geological record can tell us about that planet’s past climate and habitability.
As Ojha explained, the study of the Medusa Fossae Formation is central to understanding Mars geological history. Much like the Tharsus Montes region, this formation was formed at a time when the planet was still geologically active. “This is a massive deposit, not only on a Martian scale, but also in terms of the solar system, because we do not know of any other deposit that is like this,” he said.
Basically, sedimentary rock is the result of rock dust and debris accumulating on a planet’s surface and becoming hardened and layered over time. These layers serve as a geological record, indicating what types of processes where taking place on the surface at the time that the layers were deposited. When it comes to the Medusae Fossae Formation, scientists were unsure whether wind, water, ice or volcanic eruptions were responsible for the deposits.
In the past, radar measurements were made of the formation that suggested that Medusae Fosssae had an unusual composition. However, scientists were unsure whether the formation was made of highly porous rock or a mixture of rock and ice. For the sake of their study, Ojha and Lewis used gravity data from various Mars orbiters to measure the formation’s density for the first time.
An isolated hill in the Medusae Fossae Formation. The effect of wind erosion on this hill is evident by its streamlined shape. Credit: High Resolution Stereo Camera/European Space Agency
What they found was that the rock is unusually porous and about two-thirds as dense as the rest of the Martian crust. They also used radar and gravity data to show that the Formation’s density was too great to be explained by the presence of ice. From this, they concluded that the heavily-porous rock had to have been deposited by volcanic eruptions when Mars was still geologically active – ca. 3 billion years ago.
As these volcanoes exploded, casting ash and rock into the atmosphere, the material would have then fallen back to the surface, building up layers and streaming down hills. After enough time, the ash would have cemented into rock, which was slowly eroded over time by Martian winds and dust storms, leaving the Formation scientists see there today. According to Ojha, these new findings suggest that Mars’ interior is more complex than previously thought.
While scientists have known for some time that Mars has some volatiles – i.e. water, carbon dioxide and other elements that become gas with slight increases in temperature – in its crust that allow for periodic explosive eruptions to occur on the surface, the kind of eruption needed to create the Medusa Fossae region would have been immense. This indicates that the planet may have massive amounts of volatiles in its interior. As Ojha explained:
“If you were to distribute the Medusae Fossae globally, it would make a 9.7-meter (32-foot) thick layer. Given the sheer magnitude of this deposit, it really is incredible because it implies that the magma was not only rich in volatiles and also that it had to be volatile-rich for long periods of time.”
According to Ojha and Lewis’ study, the eruption that created the Medusa Fossae Formation would have covered Mars in a global ocean. Image: ESO/M. Kornmesser, via N. Risinger
In addition, this activity would have had a drastic impact on Mars’ past habitability. Basically, the formation of the Medusae Fossae Formation would have occurred during a pivotal point in Mars’ history. After the eruption occurred, massive amounts of carbon dioxide and (most likely) methane would have been ejected into the atmosphere, causing a significant greenhouse effect.
In addition, the authors indicated that the eruption would have ejected enough water to cover Mars in a global ocean more than 9 cm (4 inches) in thickness. This resulting greenhouse effect would have been enough to keep Mars’ surface warm to the point that the water would remain in a liquid state. At the same time, the expulsion of volcanic gases like hydrogen sulfide and sulfur dioxide would have altered the chemistry of Mars’ surface and atmosphere.
All of this would have had a drastic impact on the planet’s potential habitability. What’s more, as Kevin Lewis indicated, the new study shows that gravity surveys have the potential to interpret Mars’ geological record. “Future gravity surveys could help distinguish between ice, sediments and igneous rocks in the upper crust of the planet,” he said.
Studying Mars surface features and geological history is a lot like peeling an onion. With every layer we peel back, we get another piece of the puzzle, which together adds up to a rich and varied history. In the coming years and decades, more robotic missions will be studying the Red Planet’s surface and atmosphere in preparation for an eventual crewed mission by the 2030s.
All of these missions will allow us to learn more about Mars warmer, wetter past and whether or not may have existed there at some time (or perhaps, still does!)
