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While SpaceX’s Starlink satellites are enabling internet access and cell phone communications around the globe, they’re also posing a threat to radio astronomy, a new study suggests.
In some wavelength bands, unintended leakage of electromagnetic radiation from the latest generation of the satellites is more than 30 times brighter than emissions from previous versions, Cees Bassa, a radio astronomer at the Netherlands Institute for Radio Astronomy in Dwingeloo and his colleagues report September 18 in Astronomy & Astrophysics. Because the latest generation of Starlink satellites will orbit as many as 100 kilometers lower than earlier satellites, they’ll seem even brighter to ground-based telescopes. Overall, their brightness could easily mask observations of dimmer objects like distant galaxies or stars. More
When it comes to the expansion rate of the universe, physicists have apparently agreed to disagree.
Two types of measurements clash over how fast the cosmos is expanding (SN: 7/30/19). Now, a new estimate from the Atacama Cosmology Telescope, or ACT, further entrenches this disagreement.
To tease out the properties of the universe, ACT observes light emitted shortly after the Big Bang, known as the cosmic microwave background. Those observations reveal that the universe is expanding a rate of about 67.9 kilometers per second for each megaparsec (about 3 million light-years), physicists report in two papers posted online and submitted to arXiv.org. The number aligns with that of an earlier cosmic microwave background experiment called Planck (SN: 7/24/18).
“As an independent experiment, we see the same thing,” says cosmologist Simone Aiola of the Flatiron Institute in New York City. Located in the Atacama Desert in Chile, ACT observes the cosmic microwave background with a higher resolution than Planck did.
To measure the expansion of the universe, the Atacama Cosmology Telescope mapped out the cosmic microwave background (one portion shown). Colors represent differences in the polarization, the orientation of the light’s electromagnetic waves.ACT Collaboration
Both ACT and Planck disagree with most estimates from objects that emitted their light more recently, such as exploding stars called supernovas and bright hearts of galaxies known as quasars. Those studies tend to indicate a faster expansion rate of around 74 kilometers per second per megaparsec.
If no simple explanation can be found for the discrepancy, it could dramatically alter physicists’ understanding of the contents of the universe and how the cosmos changes over time. For example, dark energy, the shadowy stuff that causes the universe to expand at an accelerating rate, might behave differently than scientists thought.
Some researchers had speculated that an unidentified source of experimental error in the Planck data could have accounted for the mismatch. But with the independent measurement from ACT, that explanation has gone out the window. That frees physicists to focus on other explanations, like potential issues with the supernova or quasar measurements, or the possibility of unexplained new physics phenomena.
Now, says cosmologist Adam Riess of Johns Hopkins University and the Space Telescope Science Institute in Baltimore, “we can proceed without the niggling worries.” MoreA survey of small, cool stars is helping to narrow in on the conditions that might set the stage for life beyond our solar system.
A look at about 200 ultracool dwarf stars shows that they lack sufficient ultraviolet light intensity to have the potential to jump-start life, researchers report December 1 in the Monthly Notices of the Royal Astronomical Society. That may initially seem to be bad news for finding signs of alien life on distant planets. But the diminutive stars could instead serve as test beds to determine what other conditions can create the chemical foundations of life.
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}Compared with our sun, the dwarf stars in the new study are minuscule, roughly the size of Jupiter and weighing about a tenth as much as the sun. They’re also among the most common types of stars. And because they’re cool and comparatively dim, it’s often easier to spot planets orbiting them than it is in the glare of large bright stars. Astronomers studying the tiny red star TRAPPIST-1, for example, found that it hosts seven Earth-sized planets, including three that may be within the star’s habitable zone, where conditions are amenable to life (SN: 2/22/17).
For life to exist on a habitable planet, though, it must start somehow. One possibility is that UV starlight provides the energy needed to link together the hydrogen, oxygen, carbon, nitrogen, sulfur and other atoms that make up the compounds that are precursors to life.
With that in mind, space scientist Antígona Segura and colleagues used the Transiting Exoplanet Survey Satellite to measure the amount of UV radiation — among other things — emitted from 208 comparatively nearby ultracool dwarfs within 130 light-years from Earth (SN: 4/12/18). The stars they studied do emit UV light, as our sun does, and many produce bursts of UV when they let off flares. But overall, the UV energy the small stars release is too low to forge the chemicals needed to kick-start life, the team found.
The dearth of UV light doesn’t necessarily quash hopes of finding life around such stars. “UV is an energy source for prebiotic chemistry that we can measure, and that is why we focused on it,” says Segura, of the National Autonomous University of Mexico in Mexico City. “But there are many other energy sources, like cosmic and stellar particles, and particles, radiation and heat produced by radioactive decay, to name a few.”
Ultracool stars might be useful to discover whether something other than UV light can get life going. “We should search for life on the planets that have the least [UV] activity, where we can know with confidence that UV-driven prebiotic chemistry cannot happen,” says Paul Rimmer, a University of Cambridge astrophysicist who was not involved in the study. “If we find evidence of life on these [types of] planets, this will show that there are other paths to life.”
Also, Segura notes, sources of energy that could start life can also make planets less habitable for more complex life-forms. “We cannot currently say which [effects] would prevail. The best approach now is to study case by case and wait for more observational constraints, like for the case of the TRAPPIST-1 system.”
If astronomers eventually find life on planets orbiting ultracool dwarfs, it will confirm the potential for UV-free origins of life. But, Rimmer says, if it turns out that there are no signs of habitability on planets around the many small, dim dwarf stars we see, that would lower estimates of the likelihood of finding life outside our solar system. Either way, future surveys of ultracool dwarf stars could give researchers a better handle on the possible prevalence of extraterrestrial life in the universe. More
A recently found space rock is schlepping along with Earth around the sun. This “Trojan asteroid” is only the second one discovered that belongs to our planet. And it’s probably a visitor.
Trojan asteroids, which are also found accompanying Mars, Jupiter and Neptune, hang out in two locations near a planet where the gravitational pulls of that planet and the sun balance each other (SN: 10/15/21). Because of this balancing act, these locations are stable spots in space. In 2010, astronomers discovered the first known Earth Trojan — called 2010 TK7 — orbiting within one of these two regions, known as L4, tens of millions of kilometers from Earth and leading our planet around the sun (SN: 8/2/11).
Now, researchers have found another one. Dubbed 2020 XL5, this roughly 1-kilometer-wide asteroid is also at L4, astronomer Toni Santana-Ros of the University of Barcelona and colleagues report February 1 in Nature Communications.
The space rock was first spotted in December 2020, and follow-up observations suggested that it might be at L4. To confirm this, Santana-Ros and colleagues observed the asteroid using ground-based telescopes in 2021. Measurements of its brightness let the researchers estimate the asteroid’s size — about three to four times as wide as 2010 TK7. They also scoured archival data and found the object in images dating to 2012.
“There is no doubt this is an Earth Trojan,” Santana-Ros says. That decade-worth of observations let the team calculate the rock’s orbit thousands of years into the future, confirming the asteroid’s nature. It will hang around at L4 for at least 4,000 years, the team predicts. 2010 TK7, for comparison, will stick around for some 10,000 years.
Now that scientists know of two just-visiting Earth Trojans, they can envision more. The fact that the team discovered a second object means that 2010 TK7 isn’t a rarity or loner, Santana-Ros says. “It might be part of a family or population.” More
Watch out Yosemite — the moon has its own impressive rock display.
An enormous chunk of granite, measuring roughly 50 kilometers wide, may be buried beneath the lunar surface, researchers reported July 5 in Nature. Finding such a behemoth, by far the largest granite structure spotted beyond Earth, is a surprise given that forming this type of rock typically requires plate tectonics or abundant water.
When Apollo astronauts landed on the moon in the 1960s and 1970s, they encountered vistas dominated by basalt. The igneous rock is run-of-the-mill stuff on both the moon and our planet, says Matthew Siegler, a planetary scientist at the Planetary Science Institute in Tucson. “Everything starts as basalt.”
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}But over time, with enough heat and pressure, basalt can melt and morph into more durable granite. Plate tectonics and water, both mainstays on Earth, often help facilitate that transformation: Tectonic forces can help drag rocks down deep, where it’s hotter, and water, acting like a salt, helps rocks melt at lower temperatures (SN: 1/13/21).
Because the moon has no plate tectonics and very little water, finding copious amounts of granite there would be unexpected, Siegler says. Indeed, out of the roughly 380 kilograms of moon rocks (about the heft of a large bear) brought back to Earth by Apollo astronauts, just a handful of millimeter-sized pieces are granite (SN: 7/15/19). “That’s our whole inventory,” Siegler says.
But Siegler and his colleagues now have strong evidence that a massive piece of granite might be lurking under the moon’s surface. The team analyzed microwave data collected from the farside of the moon by China’s Chang’e-1 and Chang’e-2 lunar orbiters and discovered a geothermal hotspot roughly 9 degrees Celsius warmer than expected. Elevated temperatures are often an indicator of granite, Siegler says, because uranium and thorium — radioactive elements that decay over time and release heat — tend to aggregate within the rock.
To estimate how large a piece of granite could be lying beneath the region, known as the Compton-Belkovich Volcanic Complex, the researchers ran computer simulations of different sizes of granite buried at different depths. The team concluded that an ellipsoidal hunk of granite roughly 50 kilometers wide and 25 kilometers tall capped by a smaller ellipsoid of granite, all buried four kilometers below the lunar surface, best explained the Chang’e-1 and Chang’e-2 observations.
The big question is how such an edifice formed. One idea that Siegler and his colleagues propose is that a mantle plume — a column of molten rock — once persisted under the Compton-Belkovich Volcanic Complex. That plume would have turned some of the region’s basalt into granite.
On Earth, mantle plumes famously combine with tectonic plate movement to create island chains like Hawaii, Siegler says (SN: 9/19/11). But on the moon, where there is no plate tectonics, a mantle plume would just continuously heat one region, he says. “You get a single spot of the crust that keeps getting roasted.”
This is an intriguing discovery that should be followed up with a lunar mission, says Brad Jolliff, a planetary scientist at Washington University in St. Louis who was not involved with the new study. “It’s ripe for a robotic mission that has a small rover that can test some of these properties up close.”
In the next few years, scientists plan to do just that. NASA’s Lunar Vulkan Imaging and Spectroscopy Explorer mission, or Lunar-VISE, which is slated to launch by 2027, will land on the summit of one of the Gruithuisen domes. Located on the moon’s nearside, these volcanic features are believed to also contain granite. Lunar-VISE will be able to take a closeup look at the region’s chemical composition, says the mission’s principal investigator Kerri Donaldson Hanna, a planetary geologist at the University of Central Florida in Orlando.
That’s important because it’s often difficult to capture small details from orbit. Landers like Lunar-VISE can shed light on the moon’s geology, says Donaldson Hanna. “We need new observations.” More
