In the search for potentially life-supporting exoplanets, liquid water is the key indicator. Life on Earth requires liquid water, and scientists strongly believe the same is true elsewhere. But from a great distance, it’s difficult to tell what worlds have oceans of water. Some of them can have lava oceans instead, and getting the two confused is a barrier to understanding exoplanets, water, and habitability more clearly.
This brings us to K2-18b, a mini-Neptune orbiting a red dwarf (M dwarf) star about 134 light-years away. The Kepler Space Telescope found it in 2015. NASA’s Exoplanet Catalog describes it as a potentially rocky world almost nine times more massive than Earth. It takes about 30 days to complete one orbit and is about 0.1429 AU from its star.
When it was confirmed as a planet, the authors of the paper presenting the results wrote that “The planet orbiting K2-18 may be an interesting target for atmospheric studies of transiting exoplanets.”
Prophetic words, and when the JWST examined K2-18b’s atmosphere in 2023, it found the carbon-bearing molecules methane and carbon dioxide. “Webb’s discovery adds to recent studies suggesting that K2-18 b could be a Hycean exoplanet, one which has the potential to possess a hydrogen-rich atmosphere and a water ocean-covered surface,” a NASA press release said.
Planetary scientists are very interested in Hycean exoplanets. As things stand now, they’re purely hypothetical. But if scientists could confirm the existence of one of these ocean-bearing planets, the outlook for life elsewhere in our galaxy would change considerably. (If they’re not subject to the runaway greenhouse effect.) If we could reliably find a population of Hycean worlds spread out among the stars, surely that would constitute a powerful signal that life is not confined to Earth.
But there’s a lot of uncertainty regarding Hycean worlds. Do they exist? Can they hold onto their oceans, or are they too hot? Could something else explain the JWST’s atmospheric findings? Why is there a discrepancy between observation and climate modelling? The authors of a new paper point out that, observationally, K2-18b is the archetypal Hycean world. As such, it’s a good place to try to answer some of our scientific questions. The authors say that K2-13b could indeed be an ocean planet, but an ocean of lava rather than water.
The new paper is “Distinguishing oceans of water from magma on mini-Neptune K2-18b.” The lead author is Oliver Shorttle, who studies planetary chemistry at the Institute of Astronomy at Cambridge University. The paper is in pre-print and hasn’t been peer-reviewed yet.
“We propose a solution to this discrepancy between observation and climate modelling by investigating the effect of a magma ocean on the atmospheric chemistry of mini-Neptunes,” the authors write.
K2-18b is a puzzle. Its density is in between Neptune’s and Earth’s, meaning its composition is uncertain. Its density covers a range of possible compositions. JWST observations show that it has a carbon-rich atmosphere and an ammonia-poor atmosphere. These observations are both indicators of an ocean world with a thick H/He atmosphere.
Spectra of K2-18 b, obtained with Webb’s NIRISS (Near-Infrared Imager and Slitless Spectrograph) and NIRSpec (Near-Infrared Spectrograph), display an abundance of methane and carbon dioxide in the exoplanet’s atmosphere. The detection of methane and carbon dioxide and the shortage of ammonia support the hypothesis that there may be a water ocean underneath a hydrogen-rich atmosphere in K2-18 b. Image Credit: NASA, CSA, ESA, R. Crawford (STScI), J. Olmsted (STScI), Science: N. Madhusudhan (Cambridge University)
But there’s another possible explanation: a magma ocean. “We demonstrate that atmospheric NH3 depletion is a natural consequence of the high solubility of nitrogen species in magma at reducing conditions, precisely the conditions prevailing where a thick hydrogen envelope is in communication with a molten planetary surface,” the authors write.
As is so often the case when it comes to atmospheres, the availability of oxygen plays an enormous role. Oxygen is a swinger; it likes to bond with almost anything. Its presence dictates a lot of what happens in an atmosphere.
“How oxidizing a magma is has a profound effect on the solubility of nitrogen,” the authors. Nitrogen is necessary for ammonia to form since ammonia is NH3. So when the JWST found no ammonia in K2-18b’s atmosphere, it may not indicate a Hycean world after all. Instead, it may indicate a magma ocean.
The researchers used models and simulations to try to determine what the JWST observations mean for K2-18b.
This figure from the study shows the relationship between oxygen fugacity and how much nitrogen can stay in the atmosphere of a magma ocean planet. “As oxygen fugacity is decreased, nitrogen’s increased solubility depletes the atmosphere by orders of magnitude,” the authors explain. (Each coloured circle represents a model run for a given set of parameters.) Image Credit: Shorttle et al. 2024.
The researchers found that some of their modelled results of a magma ocean world agree with what the JWST found. “A set of the resulting atmospheres in the magma ocean scenario are consistent with the full transmission spectrum of K2-18b observed by JWST,” they write, adding that “this self-consistent magma ocean model can produce a qualitatively similar transmission spectrum to that observed for K2-18b, and those hypothesized for Hycean planets generally.”
If Shorttle and his colleagues are correct, then a dearth of ammonia can no longer be used to indicate the presence of an ocean on a Hycean world. Ammonia’s profile in an atmosphere can be attributed to both the magma ocean scenario and the water-world scenario. They’re not exclusive.
Artist’s depiction of a waterworld. So far, they’re only hypothetical and can be confused with magma ocean worlds. We need a way to tell them apart. Credit: David A. Aguilar (CfA)
What’s the solution?
“Thus, alternative mutually exclusive chemical tracers of the presence of a water ocean versus a magma ocean should be sought so that future observations can distinguish these potential scenarios,” the researchers write.
The authors think they may have found a chemical tracer that can do the job. They say that finding both CO2 and CO in an exoplanet atmosphere could contra-indicate a magma ocean. “One such possible tracer, and source of potential misfit of the magma ocean scenario with the observed spectrum of K2-18b, is the co-existence of CO2 and CO,” they explain. The problem is that the presence of any CO in K2-18b’s atmosphere is uncertain.
The researchers have shown that we can’t rely on the detection of carbon and the non-detection of ammonia to indicate a Hycean world because, in some circumstances, a magma ocean can produce the same atmospheric chemical profile. What can be done?
Better data and more research, of course.
“Developing clear disambiguating atmospheric tracers for the presence of liquid water versus magma
oceans is key in our quest of finding potentially habitable worlds amongst the exoplanet population,” they conclude.
NAIROBI, Kenya (AP) — The body of Ugandan Olympic athlete Rebecca Cheptegei — who died after being set on fire by her partner in Kenya — was received Friday by family and anti-femicide crusaders, ahead of her burial a day later.
Cheptegei’s family met with dozens of activists Friday who had marched to the Moi Teaching and Referral Hospital’s morgue in the western city of Eldoret while chanting anti-femicide slogans.
She is the fourth female athlete to have been killed by her partner in Kenya in yet another case of gender-based violence in recent years.
Viola Cheptoo, the founder of Tirop Angels – an organization that was formed in honor of athlete Agnes Tirop, who was stabbed to death in 2021, said stakeholders need to ensure this is the last death of an athlete due to gender-based violence.
“We are here to say that enough is enough, we are tired of burying our sisters due to GBV,” she said.
It was a somber mood at the morgue as athletes and family members viewed Cheptegei’s body which sustained 80% of burns after she was doused with gasoline by her partner Dickson Ndiema. Ndiema sustained 30% burns on his body and later succumbed.
Ndiema and Cheptegei were said to have quarreled over a piece of land that the athlete bought in Kenya, according to a report filed by the local chief.
Cheptegei competed in the women’s marathon at the Paris Olympics less than a month before the attack. She finished in 44th place.
Cheptegei’s father, Joseph, said that the body will make a brief stop at their home in the Endebess area before proceeding to Bukwo in eastern Uganda for a night vigil and burial on Saturday.
“We are in the final part of giving my daughter the last respect,” a visibly distraught Joseph said.
He told reporters last week that Ndiema was stalking and threatening Cheptegei and the family had informed police.
Four in 10 women or an estimated 41% of dating or married Kenyan women have experienced physical or sexual violence perpetrated by their current or most recent partner, according to the Kenya Demographic and Health Survey 2022.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
VICTORIA – The British Columbia government is partnering with a bear welfare group to reduce the number of bears being euthanized in the province.
Nicholas Scapillati, executive director of Grizzly Bear Foundation, said Monday that it comes after months-long discussions with the province on how to protect bears, with the goal to give the animals a “better and second chance at life in the wild.”
Scapillati said what’s exciting about the project is that the government is open to working with outside experts and the public.
“So, they’ll be working through Indigenous knowledge and scientific understanding, bringing in the latest techniques and training expertise from leading experts,” he said in an interview.
B.C. government data show conservation officers destroyed 603 black bears and 23 grizzly bears in 2023, while 154 black bears were killed by officers in the first six months of this year.
Scapillati said the group will publish a report with recommendations by next spring, while an independent oversight committee will be set up to review all bear encounters with conservation officers to provide advice to the government.
Environment Minister George Heyman said in a statement that they are looking for new ways to ensure conservation officers “have the trust of the communities they serve,” and the panel will make recommendations to enhance officer training and improve policies.
Lesley Fox, with the wildlife protection group The Fur-Bearers, said they’ve been calling for such a committee for decades.
“This move demonstrates the government is listening,” said Fox. “I suspect, because of the impending election, their listening skills are potentially a little sharper than they normally are.”
Fox said the partnership came from “a place of long frustration” as provincial conservation officers kill more than 500 black bears every year on average, and the public is “no longer tolerating this kind of approach.”
“I think that the conservation officer service and the B.C. government are aware they need to change, and certainly the public has been asking for it,” said Fox.
Fox said there’s a lot of optimism about the new partnership, but, as with any government, there will likely be a lot of red tape to get through.
“I think speed is going to be important, whether or not the committee has the ability to make change and make change relatively quickly without having to study an issue to death, ” said Fox.
This report by The Canadian Press was first published Sept. 9, 2024.
