Astronomy

To practice searching for extraterrestrial life, researchers have run a dress rehearsal with the one world they know to be habitable: Earth.
While Earth was between the sun and moon for a lunar eclipse in January 2019, the Hubble Space Telescope observed how chemicals in Earth’s atmosphere blocked certain wavelengths of sunlight from reaching the moon. That observing setup mimicked the way astronomers plan to probe the atmospheres of Earthlike exoplanets as they pass in front of their stars, filtering out some starlight.
“We basically pretend we’re alien observers looking at our planet,” says Giada Arney, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md.
Using Hubble, the researchers focused on spotting the effects of atmospheric ozone. Because ozone is both a chemical by-product of oxygen produced in photosynthesis and a shield that protects life from the sun’s harmful ultraviolet rays, astronomers think atmospheric ozone could be a key indicator that a distant world is habitable. During the lunar eclipse, Hubble examined sunlight that had passed through Earth’s atmosphere and reflected off of the moon for signatures of ozone.

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“It’s safer for Hubble to observe sunlight reflected off the moon” than to look directly at the backlit Earth, explains Allison Youngblood, an astronomer at the University of Colorado Boulder. The telescope’s instruments are so sensitive and Earth is so bright that “even the nightside would fry Hubble’s detectors.” 
Those observations revealed prominent dips in particular wavelengths of ultraviolet sunlight that had been absorbed by the ozone, Youngblood, Arney and colleagues report online August 6 in the Astronomical Journal.
The data help confirm that chemicals in the Earth’s atmosphere filter light as expected, based on researchers’ understanding of atmospheric chemistry. That finding gives astronomers more confidence that they will be able to recognize potentially habitable exoplanets. More

Mauna Kea opened, Science News, August 1, 1970 —
The new Mauna Kea Observatory of the University of Hawaii has been completed and dedication ceremonies have been held. Standing at an altitude of 13,780 feet on the island of Hawaii, the new observatory is the highest in the world. Its major instrument is an 88-inch reflecting telescope that cost $3 million to build.
Update
More than a dozen large telescopes now dot Mauna Kea, operated by a variety of organizations. Those telescopes have revolutionized astronomy, helping to reveal the accelerating expansion of the universe and evidence for the black hole at the center of the Milky Way. But the telescopes have long sparked controversy, as the dormant volcano is sacred to Native Hawaiians. Since 2014, protests have flared in response to the attempted construction of the Thirty Meter Telescope. Opponents have kept progress stalled by blocking the only access road to the site. Some scientists have spoken out against the telescope’s location. The Thirty Meter Telescope collaboration is considering the Canary Islands as a backup site. More

The closest cluster of stars to Earth is falling apart and will soon die, astronomers say.
Using the Gaia spacecraft to measure velocities of stars in the Hyades cluster and those escaping from it, researchers have predicted the cluster’s demise. “We find that there’s only something like 30 million years left for the cluster to lose its mass completely,” says Semyeong Oh, an astronomer at the University of Cambridge.
“Compared to the Hyades’ age, that’s very short,” she says. The star cluster, just 150 light-years away and visible to the naked eye in the constellation Taurus, formed about 680 million years ago from a large cloud of gas and dust in the Milky Way.
Stellar gatherings such as the Hyades, known as open star clusters, are born with hundreds or thousands of stars that are held close to one another by their mutual gravitational pull. But numerous forces try to tear them apart: Supernova explosions from the most massive stars eject material that had been binding the cluster together; large clouds of gas pass near the cluster and yank stars out of it; the stars themselves interact with one another and jettison the least massive ones; and the gravitational pull of the whole Milky Way galaxy lures stars away too. As a result, open star clusters rarely reach their billionth birthday.

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The Hyades has survived longer than many of its peers. But astronomers first saw signs of trouble there in 2018, when teams in Germany and Austria independently used the European Space Agency’s Gaia space observatory to find numerous stars that had escaped the cluster. These departing stars form two long tails on opposite sides of the Hyades — the first ever seen near an open star cluster. Each stellar tail stretches hundreds of light-years and dwarfs the cluster itself, which is about 65 light-years across.
In the new work, posted July 6 at arXiv.org, Oh and Cambridge colleague N. Wyn Evans analyzed how the cluster has lost stars over its life. It was born with about 1,200 solar masses but now has only 300 solar masses left. In fact, the two tails of escapees possess more stars than does the cluster. And the more stars the cluster loses, the less gravity it has to hold on to its remaining members, which leads to the escape of additional stars, exacerbating the cluster’s predicament.

Siegfried Röser, an astronomer at Heidelberg University in Germany who led one of the two teams that discovered the cluster’s tails, agrees that the Hyades is in its sunset years. But he worries that it’s too early to pin a precise date on the funeral. “That seems to be a little bit risky to say,” Röser says. Running a computer simulation with the stars’ masses, positions and velocities should better show what will happen in the future, he says.
The main culprit behind the cluster’s coming demise, Oh says, is the Milky Way. Just as the moon causes tides on Earth, lifting the seas on both the side facing the moon and the side facing away, so the galaxy exerts tides on the Hyades: The Milky Way pulls stars out of the side of the cluster that faces the galactic center as well as the cluster’s far side.
Even millions of years after the cluster disintegrates, its stars will continue to drift through space with similar positions and velocities, like parachutists jumping out of the same airplane. “It’s still probably going to be detectable as a coherent structure in position-velocity space,” Oh says, but the stars will be so spread out from one another that they will no longer constitute a star cluster. More

For the first time, an exoplanet family around a sunlike star has had its portrait taken. Astronomers used the Very Large Telescope in Chile to snap a photo of two giant planets orbiting a young star with about the same mass as the sun, researchers report July 22 in The Astrophysical Journal Letters.
The star, called TYC 8998-760-1, is about 300 light-years away in the constellation Musca. At just 17 million years old, the planetary family is a youngster compared with the 4-billion-year-old solar system.
Although astronomers have found thousands of exoplanets, most aren’t observed directly. Instead they are spotted as shadows crossing in front of their stars, or inferred as unseen forces tugging at their stars.
Only a few tens of planets have been photographed around other stars, and just two of those stars have more than one planet. Neither is sunlike, says astronomer Alexander Bohn of Leiden University in the Netherlands — one is more massive than the sun, the other less massive.
Both of this star’s planets are unlike anything seen in the solar system. The inner planet, a giant weighing 14 times the mass of Jupiter, is 160 times farther from its star than Earth is from the sun. The outer one weighs six times Jupiter’s mass and orbits at twice its sibling’s distance. In comparison, the Voyager 1 spacecraft, which flew past the boundary marking the sun’s magnetic influence and into interstellar space in 2012, is still closer to the sun than either planet is to its star (SN: 9/12/13).
This exoplanet family could provide new insight into how solar systems can form. “As with many other exoplanet discoveries, this discovery makes us aware of other scenarios that we did not think of,” Bohn says. More

The sun could come from a large, loose-knit clan or a small family that’s always fighting.
New computer simulations of young stars suggest two pathways to forming the solar system. The sun could have formed in a calm, large association of 10,000 stars or more, like NGC 2244 in the present-day Rosette Nebula, an idea that’s consistent with previous research. Or the sun could be from a violent, compact cluster with about 1,000 stars, like the Pleiades, researchers report July 2 in the Astrophysical Journal.Whether a star forms in a tight, rowdy cluster or a loose association can influence its future prospects. If a star is born surrounded by lots of massive siblings that explode as supernovas before a cluster spreads out, for example, that star will have more heavy elements to build planets with (SN: 8/9/19).
To nail down a stellar birthplace, astronomers have considered the solar system’s chemistry, its shape and many other factors. Most astronomers who study the sun’s birthplace think the gentle, large association scenario is most likely, says astrophysicist Fred Adams of the University of Michigan in Ann Arbor, who was not involved in the new work.
But most previous studies didn’t include stars’ motions over time. So astrophysicists Susanne Pfalzner and Kirsten Vincke, both of the Max Planck Institute for Radio Astronomy in Bonn, Germany, ran thousands of computer simulations to see how often different kinds of young stellar families produce solar systems like ours.

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The main solar system feature that the pair looked for was the distance to the farthest planet from the star. Planet-forming disks can extend to hundreds of astronomical units, or AU, the distance between the Earth and the sun (SN: 7/16/19). Theoretically, planets should be able to form all the way to the edge. But the sun’s planetary material is mostly packed within the orbit of Neptune.
“You have a steep drop at 30 AU, where Neptune is,” Pfalzner says. “And this is not what you expect from a disk.”
In 2018, Pfalzner and her colleagues showed that a passing star could have truncated and warped the solar system’s outer edge long ago. If that’s what happened, it could help point to the sun’s birth environment, Pfalzner reasoned. The key was to simulate groupings dense enough that stellar flybys happen regularly, but not so dense that the encounters happen too often and destroy disks before planets can grow up.
“We were hoping we’d get one answer,” Pfalzner says. “It turned out there are two possibilities.” And they are wildly different from each other.
Large associations have more stars, but the stars are more spread out and generally leave each other alone. Those associations can stay together for up to 100 million years. Compact clusters, on the other hand, see more violent encounters between young stars and don’t last as long. The stars shove each other away within a few million years.
“This paper opens up another channel for what the sun’s birth environment looked like,” Adams says, referring to the violent cluster notion.
The new study doesn’t cover every aspect of how a tight cluster could have affected the nascent solar system. The findings don’t account for how radiation from other stars in the cluster could erode planet-forming disks, for example, which could have shrunk the sun’s disk or even prevented the solar system from forming. The study also doesn’t explain certain heavy elements found in meteorites, which are thought to come from a nearby supernova and so could require the sun come from a long-lived stellar family.
“I think [the research] is an interesting addition to the debate,” Adams says. “It remains to be seen how the pieces of the puzzle fit together.”
Pfalzner thinks that the star cluster would break apart before radiation made a big difference, and there are other explanations for the heavy elements apart from a single supernova. She hopes future studies will be able to use that sort of cosmic chemistry to narrow the sun’s birthplace down even further.
“For us humans, this is an important question,” Pfalzner says. “It’s part of our history.” More

Get out the marshmallows and toasting sticks. The closest images yet taken of the sun show tiny flares dubbed “campfires,” astronomers announced in a news conference on July 16.
The images are the first from Solar Orbiter, a new sun-watching spacecraft that’s a joint project between NASA and the European Space Agency.
“By looking from close by, we get so much sharper images,” said David Berghmans of the Royal Observatory of Belgium in Brussels in the news conference. The pictures were better than the science team expected. “When the first images came in, the first thought was, ‘This is not possible! It cannot be that good.’”   
These never-before-seen campfire flares are thought to be little relatives of larger solar flares, powerful magnetic outbursts that shoot bright spurts of radiation into space (SN: 9/11/17). Campfire flares are a million to a billion times as small as typical solar flares. The smallest ones in the Solar Orbiter images are a few hundred kilometers across, “about the size of a European country,” Berghmans said. It’s not clear yet whether the flickers are just scaled-down solar flares, or if the two phenomena have different driving mechanisms.

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Solar physicists think campfires could help explain one of the biggest solar mysteries: why the solar corona, the sun’s wispy outer atmosphere, is millions of degrees hotter than the solar surface (SN: 8/20/17). Together, the small but ubiquitous flares could be a source of energy to the corona that astronomers haven’t accounted for.
“These campfires are totally insignificant each by themselves, but summing up their effect all over the sun, they might be the dominant contribution to the heating of the solar corona,” said Frédéric Auchère of the Institut d’Astrophysique Spatiale in Orsay, France, in a news release.
Solar Orbiter captured these pictures of “campfire” flares (indicated with arrows) on the sun in extreme ultraviolet wavelengths of light. The newly spotted flares may help heat the sun’s outer atmosphere.Solar Orbiter/EUI Team/ESA and NASA, CSL, IAS, MPS, PMOD/WRC, ROB, UCL/MSSL
Solar Orbiter launched February 9 with a suite of scientific instruments to observe the sun and its surroundings (SN: 2/9/20). The new images were taken May 30 with the Extreme Ultraviolet Imager camera when the spacecraft was 77 million kilometers from the sun, about half the distance from Earth. Berghmans and Auchère are the principal investigators for the orbiter’s ultraviolet camera.
Other spacecraft have swooped closer to the sun. The Parker Solar Probe has gotten as close as 24 million kilometers, collecting data but no direct photos because it gets too close (SN: 12/4/19). It will eventually reach 6 million kilometers from the sun’s surface. Ultimately, Solar Orbiter will come within about 42 million kilometers of the sun, and will be the first spacecraft to fly over the sun’s poles. More

The oldest disk-shaped galaxy ever spotted formed just 1.5 billion years after the Big Bang, a new study finds. That’s much earlier than astronomers thought that this type of galaxy could form. Previous observations show that disk-shaped galaxies — including sprawling, spiral systems like the Milky Way — didn’t show up in large numbers until […] More

The sun might be a magnetic slacker. A census of stars similar to the sun shows that our own star is less magnetically active than others of its kind, astrophysicists report in the May 1 Science. The result could support the idea that the sun is in a “midlife crisis,” transitioning into a quieter phase […] More