Peculiar flat regions on Saturn’s moon Titan could be the dry floors of ancient lakes and seas. The suggestion, published June 16 in Nature Communications, may solve a 20-year-old mystery. Starting in 2000, astronomers using radio telescopes on Earth have seen particularly bright radio signals coming from Titan’s equator. Those signals, called specular reflections, occur […] More

A distant galaxy has been caught in the act of shutting down.
The galaxy, called CQ 4479, is still forming plenty of new stars. But it also has an actively feeding supermassive black hole at its center that will bring star formation to a halt within a few hundred million years, astronomers reported January 11 at the virtual meeting of the American Astronomical Society. Studying this galaxy and others like it will help astronomers figure out exactly how such shutdowns happen.
“How galaxies precisely die is an open question,” says astrophysicist Allison Kirkpatrick of the University of Kansas in Lawrence. “This could give us a lot of insight into that process.”
Astronomers think galaxies typically start out making new stars with a passion. The stars form from pockets of cold gas that contract under their own gravity and ignite thermonuclear fusion in their centers. But at some point, something disrupts the cold star-forming fuel and sends it toward the supermassive black hole at the galaxy’s core. That black hole gobbles the gas, heating it white-hot. An actively feeding black hole can be seen from billions of light-years away and is known as a quasar. Radiation from the hot gas pumps extra energy into the rest of the galaxy, blowing away or heating up the remaining gas until the star-forming factory closes for good (SN: 3/5/14).

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That picture fits with the types of galaxies astronomers typically see in the universe: “blue and new” star formers, and “red and dead” dormant galaxies. But while examining data from large surveys of the sky, Kirkpatrick and colleagues noticed another type. The team found about two dozen galaxies that emit energetic X-rays characteristic of an actively gobbling black hole, but also shine in low-energy infrared light, revealing that there is still cold gas somewhere in the galaxies. Kirkpatrick and colleagues dubbed these galaxies “cold quasars” in a paper in the Sept. 1 Astrophysical Journal.
“When you see a black hole actively accreting material, you expect that star formation has already shut down,” says coauthor and astrophysicist Kevin Cooke, also of the University of Kansas, who presented the research at the meeting. “But cold quasars are in a weird time when the black hole in the center has just begun to feed.”
To investigate individual cold quasars in more detail, Kirkpatrick and Cooke used SOFIA, an airplane outfitted with a telescope that can see in a range of infrared wavelengths that the original cold quasar observations didn’t cover. SOFIA looked at CQ 4479, a cold quasar about 5.25 billion light-years away, in September 2019.
The observations showed that CQ 4479 has about 20 billion times the mass of the sun in stars, and it’s adding about 95 suns per year. (That’s a furious rate compared with the Milky Way; our home galaxy builds two or three solar masses of new stars per year.) CQ 4479’s central black hole is 24 million times as massive as the sun, and it’s growing at about 0.3 solar masses per year. In terms of percentage of their total mass, the stars and the black hole are growing at the same rate, Kirkpatrick says.
The cold quasar CQ 4479, the blue fuzzy dot at the center of this image, showed up in images taken by the Sloan Digital Sky Survey. The red dot nearby might be another galaxy interacting with CQ 4479, or it could be unrelated.K.C. Cooke et al/arxiv.org 2020, Sloan Digital Sky Survey
That sort of “lockstep evolution” runs counter to theories of how galaxies wax and wane. “You should have all your stars finish growing first, and then your black hole grows,” Kirkpatrick says. “This [galaxy] shows there’s a period that they actually do grow together.”
Cooke and colleagues estimated that in half a billion years, the galaxy will host 100 billion solar masses of stars, but its black hole will be passive and quiet. All the cold star-forming gas will have heated up or blown away.
The observations of CQ 4479 support the broad ideas of how galaxies die, says astronomer Alexandra Pope of the University of Massachusetts Amherst, who was not involved in the new work. Given that galaxies eventually switch off their star formation, it makes sense that there should be a period of transition. The findings are a “confirmation of this important phase in the evolution of galaxies,” she says. Taking a closer look at more cold quasars will help astronomers figure out just how quickly galaxies die. More

Pluto’s dark side has come into dim view, thanks to the light of the dwarf planet’s moon.

When NASA’s New Horizons spacecraft flew past Pluto in 2015, almost all the images of the dwarf planet’s unexpectedly complex surface were of the side illuminated by the sun (SN: 7/15/15). Darkness shrouded the dwarf planet’s other hemisphere. Some of it, like the area near the south pole, hadn’t seen the sun for decades.

Now, mission scientists have finally released a grainy view of the dwarf planet’s dark side. The researchers describe the process to take the photo and what it tells them about how Pluto’s nitrogen cycle affects its atmosphere October 20 in the Planetary Science Journal.

Before New Horizons passed by Pluto, the team suspected the dwarf planet’s largest moon, Charon, might reflect enough light to illuminate the distant world’s surface. So the researchers had the spacecraft turn back toward the sun to take a parting peek at Pluto.

New Horizons captured this view of the backlit dark side of Pluto as the spacecraft receded from the dwarf planet in 2015. Some light and dark splotches were illuminated by the dim light of Pluto’s moon Charon.NOIRLab, SwRI, JHUAPL, NASA

At first, the images just showed a ring of sunlight filtering through Pluto’s hazy atmosphere (SN: 7/24/15). “It’s very hard to see anything in that glare,” says planetary scientist John Spencer of the Southwest Research Institute in Boulder, Colo. “It’s like trying to read a street sign when you’re driving toward the setting sun and you have a dirty windshield.”

Spencer and colleagues took a few steps to make it possible to pull details of Pluto’s dark side out of the glare. First, the team had the spacecraft take 360 short snapshots of the backlit dwarf planet. Each was about 0.4 seconds long, to avoid overexposing the images. The team also took snapshots of the sun without Pluto in the frame so that the sun could be subtracted out after the fact.

Tod Lauer of the National Optical Astronomy Observatory in Tucson, Ariz., tried to process the images when he got the data in 2016. At the time, the rest of the data from New Horizons was still fresh and took up most of his attention, so he didn’t have the time to tackle such a tricky project.

But “it was something that just sat there and ate away at me,” Lauer says. He tried again in 2019. Because the spacecraft was moving as it took the images, each image was a little bit smeared or blurred. Lauer wrote a computer code to remove that blur from each individual frame. Then he added the reflected Charon light in each of those hundreds of images together to produce a single image.

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“When Tod did that painstaking analysis, we finally saw something emerging in the dark there … giving us a little bit of a glimpse of what the dark pole of Pluto looks like,” Spencer says.

That the team got anything at all is impressive, says planetary scientist Carly Howett, also of the Southwest Research Institute and who is on the New Horizons team but was not involved in this work. “This dataset is really, really hard to work with,” she says. “Kudos to this team. I wouldn’t have wanted to do this.”

The image, Howett says, can help scientists understand how Pluto’s frigid nitrogen atmosphere varies with its decades-long seasons. Pluto’s atmosphere is controlled by how much nitrogen is in a gas phase in the air and how much is frozen on the surface. The more nitrogen ice that evaporates, the thicker the atmosphere becomes. If too much nitrogen freezes to the ground, the atmosphere could collapse altogether.

In this image of Pluto’s sunlit side from NASA’s New Horizons spacecraft, different colors represent different kinds of ices. A faint glimpse of Pluto’s dark hemisphere in newly released mission images reveals some new details about how those ices behave.SwRI, JHUAPL, NASA

When New Horizons was there, Pluto’s south pole looked darker than the north pole. That suggests there was not a lot of fresh nitrogen frost freezing out of the atmosphere there, even though it was nearing winter. “The previous summer ended decades ago, but Pluto cools off pretty slowly,” Spencer says. “Maybe it’s still so warm [that] the frost can’t condense there, and that keeps the atmosphere from collapsing.”

There was a bright spot in the middle of the image, which could be a fresh ice deposit. That’s also not surprising, Howett says. The ices may still be moving from the north pole to the south pole as Pluto moves deeper into its wintertime.

“We’ve thought this for a long time. It makes sense,” she says. “But it’s nice to see it happening.” More

Space weather forecasting is a guessing game. Predictions of outbursts from the sun are typically based on the amount of activity observed on the sun’s roiling surface, without accounting for the specific processes behind the blasts.
But a new technique could help predict the violent eruptions of radiation known as solar flares based on the physics behind them, researchers report in the July 31 Science. When applied to old data, the method anticipated several powerful flares, although it missed some as well.
Radiation released in solar flares and associated eruptions of charged particles, or plasma,can be harmful. This space weather can disrupt radio communications, throw off satellites, take down power grids and endanger astronauts (SN: 9/11/17). More accurate forecasts could allow operators to switch off sensitive systems or otherwise make preparations to mitigate negative effects.
Current prediction methods rely on tracking flare-linked phenomena such as large, complex sunspots — dark regions on the sun’s surface with powerful magnetic fields. But that leads to some false alarms.

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In contrast, the new prediction method is rooted in the intricacies of how and when the sun’s tangled loops of magnetic fields rearrange themselves, in a process known as magnetic reconnection, releasing bursts of energy that mark solar flares.
On the sun’s surface, magnetic fields can get gnarly. Magnetic field lines, imaginary contours that indicate the direction of the magnetic field at various locations, loop and cross over one another like well-mixed spaghetti. When those lines break and reconnect, a burst of energy is released, producing a flare. The details of how and under what conditions this happens have yet to be unraveled.
In the new study, physicist Kanya Kusano from Nagoya University in Japan and colleagues propose that the largest flares result when two arcing magnetic field lines connect, forming an m-shaped loop, as a smaller loop forms close to the sun’s surface. This “double-arc instability” leads to more magnetic reconnection, and the m-shaped loop expands, unleashing energy.
Using 11 years’ worth of data from NASA’s Solar Dynamics Observatory spacecraft, the researchers identified regions on the sun with high magnetic activity. For each region, the team determined whether conditions were ripe for a flare-inducing double-arc instability, and then aimed to predict the most powerful flares the sun produces, called X-class flares. The technique correctly predicted seven of nine flares that passed a threshold that the researchers chose, called X2, the second strength subdivision of the X-class.
The successful predictions suggest that researchers may have identified the physical process that underlies some of the largest outbursts.
“Prediction is a very good benchmark for how well we can understand nature,” Kusano says.
The unsuccessful predictions are likewise illuminating: “Even if it fails, it tells us something,” says solar physicist Astrid Veronig of the University of Graz in Austria, who wrote a commentary on the result, also published in Science. The two flares that the technique missed had no associated ejection of plasma from the sun’s surface. “This kind of instability is maybe not a good way to explain these other flares,” Veronig says. They may instead have resulted from magnetic reconnection high above, instead of close to, the sun’s surface.
The mechanism on which the researchers based their prediction “is really interesting and very insightful,” says solar physicist KD Leka of NorthWest Research Associates in Boulder, Colo. But, she notes, the method couldn’t predict how soon the flares will occur — whether the burst would come an hour or a day after the right conditions first occurred — and it didn’t identify slightly weaker X1 flares, or the next class down, known as M-class flares, which could still be damaging.
“The mantra that I live by,” Leka says, “is any rule you think you’ve figured out about the sun, it’s going to figure out how to break it.” More

The lander was listening. On February 18, NASA’s InSight lander on Mars turned its attention to the landing site for another mission, Perseverance, hoping to detect its arrival on the planet.

But InSight heard nothing.

Tungsten blocks ejected by Perseverance during entry landed hard enough to create craters on the Martian surface. Collisions like these — whether from space missions or meteor strikes — send shock waves through the ground. Yet in the first experiment of its kind on another world, InSight failed to pick up any seismic waves from the blocks’ impacts, researchers report October 28 in Nature Communications.

As a result, researchers think that less than 3 percent of the energy from the impacts made its way into the Martian surface. The intensity of impact-generated rumblings varies from planet to planet and is “really important for understanding how the ground will change from a big impact event,” says Ben Fernando, a geophysicist at the University of Oxford.

Perseverance left behind several craters (one indicated with the arrow) after pieces of the mission disengaged as planned during entry, creating a rare opportunity to see how Mars absorbs energy from impacts. Univ. of Arizona, JPL-Caltech/NASA

But getting these measurements is tricky. Scientists need sensitive instruments placed relatively near an impact site. Knowing when and where a meteor will strike is nearly impossible, especially on another world.

Enter Perseverance: a hurtling space object set to hit Mars at an exact time and place (SN: 2/17/21). To help with its entry, Perseverance dropped about 78 kilograms of tungsten as the rover landed about 3,450 kilometers from InSight. The timing and weight of the drop provided a “once-in-a-mission opportunity” to study the immediate seismic effects of an impact from space, Fernando says.

The team had no idea whether InSight would be able to detect the blocks’ impacts or not, but the quiet arrival speaks volumes. “It lets us put an upper limit on how much energy from the tungsten blocks turned into seismic energy,” Fernando says. “We’ve never been able to get that number for Mars before.”

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