Enlarge / Image of a planet-forming disk, with gaps in between higher-density areas. (credit: ALMA(ESO/NAOJ/NRAO); C. Brogan, B. Saxton )

Where do planets come from? The entire process can get complicated. Planetary embryos sometimes run into obstacles to growth that leave them as asteroids or naked planetary cores. But at least one question about planetary formation has finally been answered—how they get their water.

For decades, planetary formation theories kept suggesting that planets receive water from ice-covered fragments of rock that form in the frigid outer reaches of protoplanetary disks, where light and heat from the emerging system’s star lacks the intensity to melt the ice. As friction from the gas and dust of the disk moves these pebbles inward toward the star, they bring water and other ices to planets after crossing the snow line, where things warm up enough that the ice sublimates and releases huge amounts of water vapor. This was all hypothesized until now.

NASA’s James Webb Telescope has now observed groundbreaking evidence of these ideas as it imaged four young protoplanetary disks.The telescope used its Medium-Resolution Spectrometer (MRS) of Webb’s Mid-Infrared Instrument (MIRI) to gather this data, because it is especially sensitive to water vapor. Webb found that in two of these disks, massive amounts of cold water vapor appeared past the snow line, confirming that ice sublimating from frozen pebbles can indeed deliver water to planets like ours.

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.

Enlarge / Jezero crater shows clear signs of water-formed deposits, so it's not a surprise to find water-altered material there. (credit: NASA/MSSS/USGS )

Organic chemicals, primarily composed of carbon and hydrogen, underly all of life. They're also widespread in the Universe, so they can't be taken as a clear signature of the presence of life. That creates an annoying situation regarding the search for evidence of life on Mars, which clearly has some organic chemicals despite the harsh environment.

But we don't know whether these are the right kinds of molecules to be indications of life. For the moment, we also lack the ability to tear apart Martian rocks, isolate the molecules, and figure out exactly what they are. In the meantime, our best option is to get some rough information on them and figure out the context of where they're found on Mars. And a big step has been made in that direction with the publication of results from imaging done by the Perseverance rover.

Ask SHERLOC

The instrument that's key to the new work has a name that pretty much tells you it was designed to handle this specific question: Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals (SHERLOC). SHERLOC comes with a deep-UV laser to excite molecules into fluorescing, and the wavelengths they fluoresce at can tell us something about the molecules present. It's also got the hardware to do Raman spectroscopy simultaneously.

Enlarge / An artist's illustration of NASA's two Janus spacecraft as they would have appeared in space. (credit: Lockheed Martin )

Two small spacecraft should have now been cruising through the Solar System on the way to study unexplored asteroids, but after several years of development and nearly $50 million in expenditures, NASA announced Tuesday the probes will remain locked inside a Lockheed Martin factory in Colorado.

That’s because the mission, called Janus, was supposed to launch last year as a piggyback payload on the same rocket with NASA’s much larger Psyche spacecraft , which will fly to a 140-mile-wide (225-kilometer) metal-rich asteroid—also named Psyche—for more than two years of close-up observations. Problems with software testing on the Psyche spacecraft prompted NASA managers to delay the launch by more than a year.

An independent review board set up to analyze the reasons for the Psyche launch delay identified issues with the spacecraft’s software and weaknesses in the plan to test the software before Psyche’s launch. Digging deeper, the review panel determined that NASA’s Jet Propulsion Laboratory, which manages the Psyche mission, was encumbered by staffing and workforce problems exacerbated by the COVID-19 pandemic.

Enlarge / Orbital image of the Utopia Planitia region of Mars. (credit: NASA/JPL-Caltech/Univ. of Arizona )

Most of Mars appears to be an endless expanse of alien desert, without a river or lake in sight. However, liquid water definitely existed in the planet’s distant past . A new paper has also suggested that it's also possible small quantities of water still might exist in places that otherwise appear barren.

Before China’s Zhurong (also known as Phoenix) rover went into hibernation mode last May, researchers from the National Astronomical Observatories and the Institute of Atmospheric Physics of the Chinese Academy of Sciences discovered something unexpected. Zhurong was exploring the Utopia Planitia region, which is near the planet’s equator. No liquid water was thought to exist at those latitudes. Yet when the rover beamed back data from its Multispectral Camera (MSCam), Navigation and Terrain Camera (NaTeCam), and Mars Surface Composition Detector (MarSCoDe), there was possible evidence for liquid water having been present less than half a million years ago.

“[Our findings] suggest [features] associated with the activity of saline water, indicating the existence of water process on the low-latitude region of Mars,” the researchers said in a study recently published in Science Advances.

Enlarge (credit: Simone Marchi/SwRI )

One of Earth's defining features is its plate tectonics, a phenomenon that shapes the planet's surface and creates some of its most catastrophic events, like earthquakes, tsunamis, and volcanic eruptions. While some features of plate tectonics have been spotted elsewhere in the Solar System, the Earth is the only planet we know of with the full suite of processes involved in this phenomenon. And all indications are that it started very early in our planet's history.

So what started it? Currently, two leading ideas are difficult to distinguish based on our limited evidence of the early Earth. A new study of a piece of Australia, however, argues strongly for one of them: the heavy impacts that also occurred early in the planet's history.

Options and impacts

Shortly after the Earth formed, its crust would have been composed of a relatively even layer of solid rock that acted as a lid over the still-molten mantle below. Above that, there was likely a global ocean since plate tectonics wasn't building mountains yet. Somehow, this situation was transformed into what we see now: The large regions of moving, buoyant crust of the continental plates and the constantly spreading deep ocean crust formed from mantle materials, all driven by the heat-induced motion of material through the mantle.

Enlarge / Pluto's atmosphere is fairly hazy. (credit: NASA )

Saturn’s moon Titan is distinctive, in part for its orange-ish and hazy atmosphere. It’s virtually impossible to see surface features because the haze is so opaque in the visible portion of the spectrum; what we know of it comes from things like radar imagery, instead. The haze is the product of chemical reactions in the upper atmosphere, driven by ultraviolet radiation. These then cascade into larger and more complex organic (reminder: that doesn’t mean biological) molecules.

The New Horizons mission to Pluto showed that the dwarf planet, too, has a haze. It’s less prominent in Pluto’s meager atmosphere, but it is there (it's actually similar to the one on Neptune’s moon Triton ). Because Pluto’s atmosphere isn’t that different from the upper reaches of Titan’s atmosphere, it has been thought that the same chemistry is responsible.

But a new study led by Panayotis Lavvas at the University of Reims Champagne-Ardenne shows that Pluto’s haze may require a different explanation. On both bodies, the atmosphere contains methane, carbon monoxide, and nitrogen. But if Titan’s process worked at the same rate on Pluto, it wouldn’t make enough haze particles to match what we’ve measured there. As Pluto’s atmosphere is even colder than the upper atmosphere on Titan, that haze particle chemistry should be running slower on Pluto.

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Enlarge / The instrument used to detect the water flies on a 747. (credit: NASA/Jim Ross )

Despite its proximity to a very blue planet, the Earth's Moon appeared to be completely dry, with samples returned by the Apollo missions being nearly devoid of water. But in recent years, a number of studies have turned up what appears to be water in some locations on the Moon, although the evidence wasn't always decisive.

Today, NASA is announcing that it has used an airborne observatory to spot clear indications of water in unexpected places. But the water may be in a form that makes accessing it much harder. Separately, an analysis of spots where water could be easier to reach indicates that there's more potential reservoirs than we'd previously suspected.

Up in the air

With no atmosphere and low gravity, the Moon can't hang on to water on its surface. The first time that sunlight heats lunar water up, it will form a vapor and eventually escape into space. But there are regions on the Moon, primarily near the poles, that are permanently shadowed. There, temperatures remain perpetually low, and ice can survive indefinitely. And, to test this possibility, NASA crashed some hardware into a shady area near the Moon's south pole and found water vapor amidst the debris.

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Enlarge (credit: ESA )

In recent decades, we've become aware of lots of water on Earth that's deep under ice. In some cases, we've watched this nervously, as it's deep underneath ice sheets, where it could lubricate the sheets' slide into the sea. But we've also discovered lakes that have been trapped under ice near the poles, possibly for millions of years, raising the prospect that they could harbor ancient ecosystems.

Now, researchers are applying some of the same techniques that we've used to find those under-ice lakes to data from Mars. And the results support an earlier claim that there are bodies of water trapped under the polar ice of the red planet.

Spotting liquids from orbit

Mars clearly has extensive water locked away in the forum of ice, and some of it cycles through the atmosphere as orbital cycles make one pole or the other a bit warmer. But there's not going to be pure liquid water on Mars—the temperatures just aren't high enough for very long, and the atmospheric pressures are far too low to keep any liquid water from boiling off into the atmosphere.

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