A team led by of researchers at the University of Montreal has found evidence that two exoplanets orbiting a red dwarf star are “water worlds,” where water makes up a large fraction of the entire planet. These worlds, located in a planetary system 218 light-years away in the constellation Lyra, are unlike any planets found in our solar system.
The team, led by Caroline Piaulet of the Institute for Research on Exoplanets (iREx) at the University of Montreal, published a detailed study of this planetary system, known as Kepler-138, in the journal Nature Astronomy today.
Piaulet and colleagues observed exoplanets Kepler-138c and Kepler-138d with NASA’s Hubble and the retired Spitzer space telescopes and discovered that the planets could be composed largely of water. These two planets and a smaller planetary companion closer to the star, Kepler-138b, had been discovered previously by NASA’s Kepler Space Telescope. The new study found evidence for a fourth planet, too.
Water wasn’t directly detected at Kepler-138c and d, but by comparing the sizes and masses of the planets to models, astronomers conclude that a significant fraction of their volume – up to half of it – should be made of materials that are lighter than rock but heavier than hydrogen or helium (which constitute the bulk of gas giant planets like Jupiter). The most common of these candidate materials is water.
“We previously thought that planets that were a bit larger than Earth were big balls of metal and rock, like scaled-up versions of Earth, and that’s why we called them super-Earths,” explained Björn Benneke, study co-author and professor of astrophysics at the University of Montreal. “However, we have now shown that these two planets, Kepler-138c and d, are quite different in nature and that a big fraction of their entire volume is likely composed of water. It is the best evidence yet for water worlds, a type of planet that was theorized by astronomers to exist for a long time.”
With volumes more than three times that of Earth and masses twice as big, planets c and d have much lower densities than Earth. This is surprising because most of the planets just slightly bigger than Earth that have been studied in detail so far all seemed to be rocky worlds like ours. The closest comparison, say researchers, would be some of the icy moons in the outer solar system that are also largely composed of water surrounding a rocky core.
“Imagine larger versions of Europa or Enceladus, the water-rich moons orbiting Jupiter and Saturn, but brought much closer to their star,” explained Piaulet. “Instead of an icy surface, they would harbor large water-vapor envelopes.”
Researchers caution the planets may not have oceans like those on Earth directly at the planet’s surface. “The temperature in Kepler-138d’s atmosphere is likely above the boiling point of water, and we expect a thick, dense atmosphere made of steam on this planet. Only, under that steam atmosphere there could potentially be liquid water at high pressure, or even water in another phase that occurs at high pressures, called a supercritical fluid,” Piaulet said.
In 2014, data from NASA’s Kepler Space Telescope allowed astronomers to announce the detection of three planets orbiting Kepler-138. This was based on a measurable dip in starlight as the planet momentarily passed in from of their star.
This illustration shows cross-sections of the Earth and the exoplanet Kepler-138d. Measurements of Kepler-138d’s density suggest it could have a water layer that makes up more than 50% of its volume, to a depth of about 1,243 miles (2,000 kilometers). Credit: Benoit Gougeon (University of Montreal)
Benneke and his colleague Diana Dragomir, from the University of New Mexico, came up with the idea of re-observing the planetary system with the Hubble and Spitzer space telescopes between 2014 and 2016 to catch more transits of Kepler-138d, the third planet in the system, in order to study its atmosphere.
A new exoplanet in the system
The two possible water worlds, Kepler-138c and d, are not located in the habitable zone, the area around a star where temperatures would allow liquid water on the surface of a rocky planet. But in the Hubble and Spitzer data, researchers additionally found evidence for a new planet in the system, Kepler-138e, in the habitable zone.
This newly found planet is small and farther from its star than the three others, taking 38 days to complete an orbit. The nature of this additional planet, however, remains an open question because it does not seem to transit its host star. Observing the exoplanet’s transit would have allowed astronomers to determine its size.
With Kepler-138e now in the picture, the masses of the previously known planets were measured again via the transit timing-variation method, which consists of tracking small variations in the precise moments of the planets’ transits in front of their star caused by the gravitational pull of other nearby planets.
The researchers had another surprise: They found that the two water worlds Kepler-138c and are “twin” planets, with virtually the same size and mass, while they were previously thought to be drastically different. The closer-in planet, Kepler-138b, on the other hand, is confirmed to be a small Mars-mass planet, one of the smallest exoplanets known to date.
“As our instruments and techniques become sensitive enough to find and study planets that are farther from their stars, we might start finding a lot more of these water worlds,” Benneke concluded.
More About the Mission
The entire body of scientific data collected by Spitzer during its lifetime is available to the public via the Spitzer data archive, housed at the Infrared Science Archive at IPAC at Caltech in Pasadena, California. NASA’s Jet Propulsion Laboratory, a division of Caltech, managed Spitzer mission operations for the agency’s Science Mission Directorate in Washington. Science operations were conducted at the Spitzer Science Center at IPAC at Caltech. Spacecraft operations were based at Lockheed Martin Space in Littleton, Colorado.
For more information about NASA’s Spitzer mission, go to:
Astrobiology, Avatar, Avatar The Way Of Water
An asteroid will whip by Earth tomorrow in one of closest approaches ever recorded
An asteroid the size of a delivery truck will whip past Earth on Thursday night, one of the closest such encounters ever recorded.
NASA insists it will be a near miss with no chance of the asteroid hitting Earth.
The U.S. space agency said Wednesday that this newly discovered asteroid will zoom 3,600 kilometres above the southern tip of South America. That’s 10 times closer than the bevy of communication satellites circling overhead.
The closest approach will occur at 7:27 p.m. ET.
Even if the space rock came a lot closer, scientists said most of it would burn up in the atmosphere, with some of the bigger pieces possibly falling as meteorites.
NASA’s impact hazard assessment system, called Scout, quickly ruled out a strike, said its developer, Davide Farnocchia, an engineer at the agency’s Jet Propulsion Laboratory in Pasadena, Calif.
“But despite the very few observations, it was nonetheless able to predict that the asteroid would make an extraordinarily close approach with Earth,” Farnocchia said in a statement.
“In fact, this is one of the closest approaches by a known near-Earth object ever recorded.”
Asteroid spotted by amateur astronomer in Crimea
Discovered Saturday, the asteroid known as 2023 BU is believed to be 3.5 to 8.5 metres across.
It was first spotted by Gennady Borisov, the same amateur astronomer in Crimea who discovered an interstellar comet in 2019.
Within a few days, dozens of observations were made by astronomers around the world, allowing them to refine the asteroid’s orbit.
The asteroid’s path will be drastically altered by Earth’s gravity once it zips by. Instead of circling the sun every 359 days, it will move into an oval orbit lasting 425 days, according to NASA.
Nuclear-powered spaceships? U.S. plans for 2027
The United States plans to test a spacecraft engine powered by nuclear fission by 2027 as part of a long-term NASA effort to demonstrate more efficient methods of propelling astronauts to Mars in the future, the space agency’s chief said on Tuesday.
NASA will partner with the U.S. military’s research and development agency, DARPA, to develop a nuclear thermal propulsion engine and launch it to space “as soon as 2027,” NASA administrator Bill Nelson said during a conference in National Harbor, Maryland.
The U.S. space agency has studied for decades the concept of nuclear thermal propulsion, which introduces heat from a nuclear fission reactor to a hydrogen propellant in order to provide a thrust believed to be far more efficient than traditional chemical-based rocket engines.
NASA officials view nuclear thermal propulsion as crucial for sending humans beyond the moon and deeper into space. A trip to Mars from Earth using the technology could take roughly four months instead of some nine months with a conventional, chemically powered engine, engineers say.
That would substantially reduce the time astronauts would be exposed to deep-space radiation and would also require fewer supplies, such as food and other cargo, during a trip to Mars.
“If we have swifter trips for humans, they are safer trips,” NASA deputy administrator and former astronaut Pam Melroy said Tuesday.
The planned 2027 demonstration, part of an existing DARPA research program that NASA is now joining, could also inform the ambitions of the U.S. Space Force, which has envisioned deploying nuclear reactor-powered spacecraft capable of moving other satellites orbiting near the moon, DARPA and NASA officials said.
DARPA in 2021 awarded funds to General Atomics, Lockheed Martin and Jeff Bezos’ space company Blue Origin to study designs of nuclear reactors and spacecraft. By around March, the agency will pick a company to build the nuclear spacecraft for the 2027 demonstration, the program’s manager Tabitha Dodson said in an interview.
The joint NASA-DARPA effort’s budget is US$110 million for fiscal year 2023 and is expected to be hundreds of millions of dollars more through 2027.
Reporting by Joey Roulette; Editing by Chizu Nomiyama and David Gregorio
The green comet ZTF returns to the solar system 50,000 years later… and it will be visible from Earth
For astronomy enthusiasts, February 1 is marked in red on their calendars. The reason: it is not every day that there is a chance to see a green comet.
In fact, it is the first time in 50,000 years that C/2022 ZTF will return to the solar system. And it will be early next month when it will reach its closest position to Earth.
Specifically, the green comet ZTF will pass 42 million light years from our planet. Experts are not 100 percent sure whether it will be visible from the surface without the use of any instrument. However, if we have specific astronomy binoculars or telescopes, we will be able to see it without any problem.
As usually happens in these cases, the best places to observe the comet, this one or any other, are places with little artificial light. That is to say, we should move away from urban centres and it is preferable to do so in the hours before dawn.
Why is comet ZTF green?
Comet ZTF has a brightness and a colour that, although not unique, is clearly distinctive. Its hue is due to the fact that it is composed, among other materials, of diatomic carbon.
When it comes into contact with sunlight, the decomposition of this element causes the gas to acquire this spectacular colour.
Comet ZTF was discovered in March 2022
Frank Masci and Bryce Bolin of the Palomar Observatory in California were responsible for spotting the striking comet ZTF in the sky. It is so named because its discovery is part of the Zwicky Transient Facility surveillance programme, which uses the powerful Schmidt telescope at the facility.
Initially, the scientists responsible for the discovery thought it was an asteroid, but they quickly realised that this was not the case. Despite the striking colour of this comet, experts advise keeping expectations low. In any case, it is an event that has aroused great interest in the community.
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