200 light-years away from Earth, there’s a K-type main-sequence star named TOI (TESS Object of Interest) 178. When Adrian Leleu, an astrophysicist at the Center for Space and Habitability of the University of Bern, observed it, it appeared to have two planets orbiting it at roughly the same distance. But that turned out to be incorrect. In fact, six exoplanets orbit the smallish star.
And five of those six are locked into an unexpected orbital configuration.
Five of the planets are engaged in a rare rhythmic, dance around the star. In astronomical terms, they’re in an unusual orbital resonance, which means their orbits around their star display repeated patterns. That property makes them an intriguing object of study and one that could tell us a lot about how planets form and evolve.
“Through further observations, we realized that there were not two planets orbiting the star at roughly the same distance from it, but rather multiple planets in a very special configuration.”
Adrian Leleu, Center for Space and Habitability, University of Bern.
In the team’s initial observations, it appeared there were only two planets, as five of them move in such a way as to deceive the eye. But further observations showed that something else was happening in the system. “Through further observations, we realized that there were not two planets orbiting the star at roughly the same distance from it, but rather multiple planets in a very special configuration,” said lead author Leleu.
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In this artist’s animation, the rhythmic movement of the planets around the central star is represented through a musical harmony, created by attributing a note (in the pentatonic scale) to each of the planets in the resonance chain. This note plays when a planet completes either one full orbit or one half orbit; when planets align at these points in their orbits, they ring in resonance. Credit: ESO
TOI-178’s orbital resonance is similar to another familiar orbital resonance right here in our own Solar System. That one encompasses Jupiter’s moons Io, Europa, and Ganymede.
The orbital resonance shared by Ganymede, Europa, and Io is fairly simple. Io makes four full orbits for every single orbit of Ganymede and two full orbits for Europa’s full orbit. But the planets around TOI-178 have a much more complex relationship.
TOI-178’s five outer planets are in a 18:9:6:4:3 chain of resonance. The first in the chain and second from the star completes 18 orbits, the second in the chain and third from the star completes 9 orbits, and it continues on from there. The closest planet to the star isn’t part of the chain.
For a system to be orbiting its star in such an orderly and predictable fashion, conditions had to be relatively sedate in this system. Giant impacts or planet migrations would have disrupted it. “The orbits in this system are very well ordered, which tells us that this system has evolved quite gently since its birth,” explained co-author Yann Alibert from the University of Bern.
But there’s more.
In our Solar System the small inner planets are all rocky, while the planets in the outer Solar System are large and gaseous. Beyond Neptune is a region of ice dwarf planets and Kuiper Belt Objects. Image credit: NASA/JPL/IAU
In our Solar System, the inner planets are rocky, and the planets beyond the asteroid belt are not; they’re gaseous. This is one of those instances where we might be tempted to think our Solar System represents some sort of norm. But the TOI-178 system is much different. Gaseous and rocky planets are not delineated like in our system.
“It appears there is a planet as dense as the Earth right next to a very fluffy planet with half the density of Neptune, followed by a planet with the density of Neptune. It is not what we are used to,” said Nathan Hara from the Université de Genève, Switzerland, one of the researchers involved in the study.
“This contrast between the rhythmic harmony of the orbital motion and the disorderly densities certainly challenges our understanding of the formation and evolution of planetary systems,” says Leleu.
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The team used some of the European Observatory’s most advanced, flagship instruments in this work. The ESPRESSO instrument on the VLT, and the NGTS and SPECULOOS instruments at the ESO’s Paranal Observatory. They also used the European Space Agency’s CHEOPS exoplanet satellite. These instruments all specialize in one way or another with the study of exoplanets, which are virtually impossible to detect with a “regular” telescope.
Exoplanets are a long way away from Earth, and the overpowering light from their stars makes them nearly invisible in a regular optical telescope.
The instruments used in this study detect and characterize exoplanets in a couple of different ways. But it all comes down to detecting light. The transiting method used by the NGTS (Next-Generation Transit Survey), CHEOPS (Characterizing ExOPlanet Satellite), and SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars) detect the dip in starlight when an exoplanet passes in front of its star. The radial velocity method employed by ESPRESSO detects shifts in the starlight’s normal spectrum when an exoplanet tugs on the star and shifts its position ever so slightly.
By using multiple instruments with different methods and capabilities, the team was able to characterize the system in detail. The innermost planet in the system, which is not in resonance with the others, moves the fastest. It completes an orbit in just two Earth days. The slowest planet moves ten times slower than that. The planet sizes range from one to three Earth sizes, and the masses range from 1.5 to thirty times Earth’s mass.
The orbital resonance of the planets is in an exquisite balance. The authors write that “The orbital configuration of TOI-178 is too fragile to survive giant impacts, or even significant close encounters… a sudden change in period of one of the planets of less than a few .01 d can render the system chaotic.” They also write that their data “…shows that modifying a single period axis can break the resonant structure of the entire chain.”
This discovery just means more work for astronomers. The unusual orbital resonance and positions of the planets means they need to rethink some of our theories around the formation and evolution of planets and solar systems.
This figure from the study compares the density, mass, and equilibrium temperature of the TOI-178 planets with other exoplanet systems. In Kepler-60, Kepler-80, and Kepler-223, the density of the planets decreases when the equilibrium temperature decreases. Contrary to the three Kepler systems, in the TOI-178 system, the density of the planets is not a growing function of the equilibrium temperature. The team behind this study says that if they can understand why the TOI-178 system is different, it could become a sort of Rosetta Stone for deciphering solar system and planetary development. Image Credit: Leleu et al, 2021.
As the authors write in their paper: “Determining the architecture of multi-planetary systems is one of the cornerstones of understanding planet formation and evolution. Resonant systems are especially important as the fragility of their orbital configuration ensures that no significant scattering or collisional event has taken place since the earliest formation phase when the parent protoplanetary disc was still present.”
The nebular hypothesis, also called the Solar Nebular Disk Model (SNDM), is the working theory for the formation of our Solar System and others. According to the model, a giant molecular cloud undergoes gravitational collapse, and when enough gas gathers together, it eventually begins fusion, and a star’s life begins. Most of the material in the cloud will be taken up by the star, and in our Solar System, the Sun has the lion’s share: about 99.86%.
The remaining material makes up the protoplanetary disk, which rotates around the star in a flattened pancake shape. As material clumps together in the rotating protoplanetary disk, it eventually forms planets. There are some problems with the nebular hypothesis, and other theories have tried to explain them.
These are images of nearby protoplanetary disks. At the center of each one is a young star, and the gaps are in the disks are caused by forming exoplanets. Credit: ALMA (ESO/NAOJ/NRAO), S. Andrews et al.; NRAO/AUI/NSF, S. Dagnello
But this system challenges that theory. The SNDM suggests that rocky, terrestrial planets form nearer the star. They start out as planetary embryos and through violent mergers create planets like Venus, Mercury, Mars, and Earth. Gas giants, according to the SNDM, form out beyond the Solar System’s frost line, where planet embryos form out of frozen volatiles.
But the TOI-178 system challenges that understanding. If the planets in that system followed the SNDM, then the gas planets would be further from the star, and the rocky planets would be closer. Since they’re not, something must have disrupted them. But if something disrupted them, their orbits wouldn’t be choreographed in such an exquisite rhythm. It’s a conundrum.
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“Understanding, in a single framework, the apparent disorder in terms of planetary density on one side and the high level of order seen in the orbital architecture on the other side will be a challenge for planetary system formation models,” they write.
Systems like this are challenging to understand, but ultimately, they drive researchers to think harder and to observe more fully.
As the team of scientists write in their conclusion: “The TOI-178 system, as revealed by the recent observations described in this paper, contains a number of very important features: Laplace resonances, variation in densities from planet to planet, and a stellar brightness that allows a number of followup observations (photometric, atmospheric, and spectroscopic). It is therefore likely to become one of the Rosetta Stones for understanding planet formation and evolution, even more so if additional planets continuing the chain of Laplace resonances is discovered orbiting inside the habitable zone.”
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.
