Most of the gas in the Universe is a mixture of hydrogen and helium. It's thought that the initial atmospheres of most planets also start out that way. However, over billions of years, as planets evolve, the composition of their atmospheres may shift. Hydrogen can react with other chemicals, and both it and helium can be lost to space. Venus, Earth, and Mars are thought to have second atmospheres, with their original hydrogen/helium envelopes having been lost and/or transformed.
The dynamics of loss are complicated. Lighter elements are lost more easily, but hydrogen can be protected by being incorporated into molecules like methane and ammonia. The gravity of the body can help retain some molecules, and a magnetic field can limit radiation's ability to blast material out of the atmosphere. Proximity to a star will matter too, both because of the radiation it produces and because it can heat the atmosphere and expand it to where gravity's influence is less substantial.
Given all these complications, it can be difficult to know what to expect to find on exoplanets. But a study in Wednesday's issue of Nature describes observations of helium being lost from the atmosphere of an exoplanet orbiting the star LHS 1140, about 50 light-years away. Based on the rate at which the helium is being lost, we can infer something about the remaining atmosphere.
WD 1856 b is the only confirmed case of a planet that survived the death of a Sun-like star. It’s a Jupiter-size world orbiting a white dwarf—the burned-out remnant of a Sun-like star. Now, a team of astronomers has used the James Webb Space Telescope to take a closer look at this planet for the first time, and what they found makes an already strange system even stranger.
A feeding frenzy
WD 1856 b was an accidental discovery. Astronomers pointed the TESS observatory at a sample of roughly 2,000 white dwarfs in 2020. These stars are the remains of a Sun-like star that have already gone through a red-giant phase, leaving behind an Earth-size body that’s primarily composed of elements like carbon and oxygen. The TESS team was searching for small objects like comets or asteroids that might transit across the face of these dead stars.
What they found in the WD 1856 system was a gas giant. “As soon as they looked at it, they said, okay, that’s weird,” said Christopher O’Connor, a theoretical astrophysicist at Cornell University and co-author of the recent Nature study on WD 1856 b.
Earth is the only planet we know of with buoyant, silica-rich continents. But, despite decades of research, geologists still don't agree on how they formed. "The continents started appearing around about four billion years ago—that's the oldest continental rock we know about,” said Tim Johnson, a geologist at Curtin University in Perth, Australia. “The Earth is four and a half billion years old, so why they started appearing then is unknown, as is the mechanism to make that continental crust."
Johnson and his colleagues are now arguing that the formation of continents on Earth was caused largely by an intense, sustained barrage of asteroid impacts that kept the early crust hot and thin enough to make buoyant continents possible. In short, the lands we live on are here because of ancient bombardment from space.
Plates and plumes
The problem with studying the formation of continents is that the geological evidence of this process is almost gone. The oldest known continental-type rocks crystallized around 4.03 billion years ago, right at the end of the Hadean eon (the earliest era in Earth’s history, spanning the first 500 million years of its existence). Rare basaltic rocks date back about 4.2 billion years, and a handful of the oldest zircon crystals push the record back to 4.4 billion years. Beyond that, there's hardly anything else. So, scientists looking into the origin of continents had to rely largely on educated guesses. “There are huge debates about what was going on in the early Earth, because the data is so scarce,” Johnson said.
Having a computer strapped to my face for 40 minutes was one reason to feel a little sweaty. But the tour of the Universe I had just received in virtual reality—including visits to the near vicinity of the Sun, the giant black hole at the center of our galaxy, and a hellscape of an exoplanet 41 light-years distant—provided another excuse for sensing some heat.
Smithsonian Starstruck: An Immersive Experience is a 40-minute astronomy walk-through. It debuted in Washington, DC, in May with solo adult tickets now ranging from $29 to $35 and group tickets for four or more starting at $18 each (all now discounted by 15 percent); it will also open in Denver, Orlando, Florida, and San Antonio, Texas, later this year. I stopped by on a Monday in June to take it in.
After some onboarding that included setting such preferences as closed captioning and signing a waiver, I had enough time to sit on a bench next to the exhibit space (which has hosted other VR experiences) to enjoy watching another attendee with a VR headset blurt out, “Oh my God!”
Stars in the constellation Lupus glitter in an image from the Vera C. Rubin Observatory. The full-resolution version of the image amounts to 1.7 gigapixels. (Credit: NSF–DOE Vera C. Rubin Observatory / NOIRLab / SLAC / AURA)
The start of the Legacy Survey of Space and Time, or LSST, follows years of planning and construction of the billion-dollar observatory in Chile. Scientists celebrated the completion of the construction phase with a “First Look” batch of pictures a year ago, and then turned to preparing for the LSST in earnest.
In February, the Rubin team turned on the observatory’s Alert Production Pipeline, which can send out millions of notifications about potentially noteworthy astronomical phenomena. That set the stage for what some have compared to filming a time-lapse movie of the cosmos.
“Today, we begin filming the greatest cosmic movie ever made. This moment reflects decades of vision, innovation and the power of federal investment in science through the U.S. National Science Foundation and the Department of Energy,” acting NSF Director Brian Stone said in a news release. “Every night, NSF-DOE Rubin Observatory will expand the frontiers of knowledge and strengthen America’s global leadership in science and innovation.”
Researchers at the University of Washington have played a key role in the project, primarily by developing software tools for analyzing the terabytes of data that the observatory is expected to produce on a nightly basis. That work is done at UW’s Institute for Data Intensive Research in Astrophysics and Cosmology, also known as the DiRAC Institute.
UW astronomer Zeljko Ivezić, who heads up the LSST campaign, helped determine when the observatory was ready for the survey.
“The decision to officially begin the LSST was made after a period of system optimization and a careful operational review of technical readiness, data system performance and scientific validation,” he said. Among the factors considered were image quality, effective survey speed, system reliability and calibration accuracy.
The observatory makes use of the world’s largest digital camera (3,200 megapixels per image) to capture a fresh picture every 40 seconds. If the skies over Chile are clear, the entire southern sky can be photographed over the course of just a few nights. Then Rubin begins the next round of picture-taking.
The concept for the observatory began with discussions among astronomers in the 1990s, and picked up steam in 2007 when Seattle-area tech pioneer Charles Simonyi and Microsoft co-founder Bill Gates contributed a total of $30 million to the project. In 2020, the observatory was named after the late astronomer Vera Rubin — and its 8.4-meter (27.5-foot) telescope was dubbed the Simonyi Survey Telescope in honor of Simonyi’s family.
To celebrate the start of the survey, the Rubin Observatory team released a 1.7-gigapixel image featuring an “ocean of stars” in the constellation Lupus. “The faint, glowing clouds spread across this image are galactic cirrus: clouds of interstellar gas and dust that can be seen in the foreground of the Milky Way,” the team said in an image advisory.
Distant stars aren’t Rubin’s only targets. The survey is also expected to supercharge the search for small bodies in our own solar system. During preparations for the LSST, the Rubin team reported the discovery of more than 11,000 previously unseen asteroids. And that’s just the start: A computer simulation suggests that the survey could map more than 5 million asteroids.
Rubin’s observations could even shed light on the nature of dark matter and dark energy, invisible components of the cosmos that together make up more than 95 percent of the universe’s mass-energy content.
Scientists say the key to Rubin’s success will be the ability to track changes in the night sky over the course of 10 years.
“With its world-class design and tools, Rubin Observatory will capture the dynamic nature of our cosmos and reveal unimagined insights into our universe’s biggest mysteries, from our own solar system to the very structure of the universe,” said Dario Gil, undersecretary for science at the U.S. Department of Energy. “By seeking to understand the enigmatic phenomena of dark energy and dark matter, we are not just observing the stars; we are striving to grasp the fundamental laws that govern our existence.”
The Vera C. Rubin Observatory is a joint initiative of NSF and the U.S. Department of Energy’s Office of Science, and is operated jointly by NSF NOIRLab and SLAC National Accelerator Laboratory.
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