Connect with us

Space

Lots of Tatooine-like planets around binary stars may be habitable

Published

on

011723_jr_binary-stars_feat_REV.jpg



SEATTLE — Luke Skywalker’s home planet in Star Wars is the stuff of science fiction. But Tatooine-like planets in orbit around pairs of stars might be our best bet in the search for habitable planets beyond our solar system.

Many stars in the universe come in pairs. And lots of those should have planets orbiting them (SN: 10/25/21). That means there could be many more planets orbiting around binaries than around solitary stars like ours. But until now, no one had a clear idea about whether those planets’ environments could be conducive to life. New computer simulations suggest that, in many cases, life could imitate art.

Earthlike planets orbiting some configurations of binary stars can stay in stable orbits for at least a billion years, researchers reported January 11 at the American Astronomical Society meeting. That sort of stability, the researchers propose, would be enough to potentially allow life to develop, provided the planets aren’t too hot or cold.

Advertisement

Of the planets that stuck around, about 15 percent stayed in their habitable zone — a temperate region around their stars where water could stay liquid — most or even all of the time.

The researchers ran simulations of 4,000 configurations of binary stars, each with an Earthlike planet in orbit around them. The team varied things like the relative masses of the stars, the sizes and shapes of the stars’ orbits around each other, and the size of the planet’s orbit around the binary pair.

The scientists then tracked the motion of the planets for up to a billion years of simulated time to see if the planets would stay in orbit over the sorts of timescales that might allow life to emerge.

A planet orbiting binary stars can get kicked out of the star system due to complicated interactions between the planet and stars. In the new study, the researchers found that, for planets with large orbits around star pairs, only about 1 out of 8 were kicked out of the system. The rest were stable enough to continue to orbit for the full billion years. About 1 in 10 settled in their habitable zones and stayed there.

Of the 4,000 planets that the team simulated, roughly 500 maintained stable orbits that kept them in their habitable zones at least 80 percent of the time.

Advertisement

“The habitable zone . . . as I’ve characterized it so far, spans from freezing to boiling,” said Michael Pedowitz, an undergraduate student at the College of New Jersey in Ewing who presented the research. Their definition is overly strict, he said, because they chose to model Earthlike planets without atmospheres or oceans. That’s simpler to simulate, but it also allows temperatures to fluctuate wildly on a planet as it orbits.

“An atmosphere and oceans would smooth over temperature variations fairly well,” says study coauthor Mariah MacDonald, an astrobiologist also at the College of New Jersey. An abundance of air and water would potentially allow a planet to maintain habitable conditions, even if it spent more of its time outside of the nominal habitable zone around a binary star system.

The number of potentially habitable planets “will increase once we add atmospheres,” MacDonald says, “but I can’t yet say by how much.”

She and Pedowitz hope to build more sophisticated models in the coming months, as well as extend their simulations beyond a billion years and include changes in the stars that can affect conditions in a solar system as it ages.

Advertisement

The possibility of stable and habitable planets in binary star systems is a timely issue says Penn State astrophysicist Jason Wright, who was not involved in the study.

“At the time Star Wars came out,” he says, “we didn’t know of any planets outside the solar system, and wouldn’t for 15 years. Now we know that there are many and that they orbit these binary stars.”

These simulations of planets orbiting binaries could serve as a guide for future experiments, Wright says. “This is an under-explored population of planets. There’s no reason we can’t go after them, and studies like this are presumably showing us that it’s worthwhile to try.”



Source link

Advertisement

Space

The Kuiper Belt’s dwarf planet Quaoar hosts an impossible ring

Published

on

By

020823_lg_Quaoar_feat.jpg



The dwarf planet Quaoar has a ring that is too big for its metaphorical fingers. While all other rings in the solar system lie within or near a mathematically determined distance of their parent bodies, Quaoar’s ring is much farther out.

“For Quaoar, for the ring to be outside this limit is very, very strange,” says astronomer Bruno Morgado of the Federal University of Rio de Janeiro. The finding may force a rethink of the rules governing planetary rings, Morgado and colleagues say in a study published February 8 in Nature.

Quaoar is an icy body about half the size of Pluto that’s located in the Kuiper Belt at the solar system’s edge (SN: 8/23/22). At such a great distance from Earth, it’s hard to get a clear picture of the world.

Advertisement

So Morgado and colleagues watched Quaoar block the light from a distant star, a phenomenon called a stellar occultation. The timing of the star winking in and out of view can reveal details about Quaoar, like its size and whether it has an atmosphere.

The researchers took data from occultations from 2018 to 2020, observed from all over the world, including Namibia, Australia and Grenada, as well as space. There was no sign that Quaoar had an atmosphere. But surprisingly, there was a ring. The finding makes Quaoar just the third dwarf planet or asteroid in the solar system known to have a ring, after the asteroid Chariklo and the dwarf planet Haumea (SN: 3/26/14; SN: 10/11/17).

Even more surprisingly, “the ring is not where we expect,” Morgado says.

Known rings around other objects lie within or near what’s called the Roche limit, an invisible line where the gravitational force of the main body peters out. Inside the limit, that force can rip a moon to shreds, turning it into a ring. Outside, the gravity between smaller particles is stronger than that from the main body, and rings will coalesce into one or several moons.

“We always think of [the Roche limit] as straightforward,” Morgado says. “One side is a moon forming, the other side is a ring stable. And now this limit is not a limit.”

Advertisement

For Quaoar’s far-out ring, there are a few possible explanations, Morgado says. Maybe the observers caught the ring at just the right moment, right before it turns into a moon. But that lucky timing seems unlikely, he notes.

Maybe Quaoar’s known moon, Weywot, or some other unseen moon contributes gravity that holds the ring stable somehow. Or maybe the ring’s particles are colliding in such a way that they avoid sticking together and clumping into moons.

The particles would have to be particularly bouncy for that to work, “like a ring of those bouncy balls from toy stores,” says planetary scientist David Jewitt of UCLA, who was not involved in the new work.

The observation is solid, says Jewitt, who helped discover the first objects in the Kuiper Belt in the 1990s. But there’s no way to know yet which of the explanations is correct, if any, in part because there are no theoretical predictions for such far-out rings to compare with Quaoar’s situation.

That’s par for the course when it comes to the Kuiper Belt. “Everything in the Kuiper Belt, basically, has been discovered, not predicted,” Jewitt says. “It’s the opposite of the classical model of science where people predict things and then confirm or reject them. People discover stuff by surprise, and everyone scrambles to explain it.”

Advertisement

More observations of Quaoar, or more discoveries of seemingly misplaced rings elsewhere in the solar system, could help reveal what’s going on.

“I have no doubt that in the near future a lot of people will start working with Quaoar to try to get this answer,” Morgado says.



Source link

Advertisement
Continue Reading

Space

Charon’s Freezing Ocean Produced Huge Canyons on Its Surface, Modeling Study Suggests | Sci.News

Published

on

By

image_11635-Charon.jpg


When ocean-bearing moons begin to cool down, their oceans can freeze. As new ice accretes to the bottom of the existing ice shell, the added volume of the ice can stress the shell. Pluto’s largest moon, Charon, has canyons and cryovolcanic flows that may have formed in response to a freezing ocean. In new research, planetary scientists from the Southwest Research Institute, the University of California, Davis, and the University of California, Berkeley modeled the formation of fractures within Charon’s ice shell as the ocean underneath it freezes to explore the evolution of the moon’s interior and surface. They found that an ocean source for cryovolcanic flows is unlikely because the ice shell would have had to be much thinner than current thermal evolution models imply; however, freezing the ocean may have produced the stresses that formed canyons later in Charon’s history.
Rhoden et al. revisited New Horizons data to explore the source of cryovolcanic flows and an obvious belt of fractures on Charon. Image credit: NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute.

Rhoden et al. revisited New Horizons data to explore the source of cryovolcanic flows and an obvious belt of fractures on Charon. Image credit: NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute.

“A combination of geological interpretations and thermal-orbital evolution models implies that Charon had a subsurface liquid ocean that eventually froze,” said Dr. Alyssa Rhoden, a researcher at the Southwest Research Institute.

Advertisement

“When an internal ocean freezes, it expands, creating large stresses in its icy shell and pressurizing the water below.”

“We suspected this was the source of Charon’s large canyons and cryovolcanic flows.”

New ice forming on the inner layer of the existing ice shell can also stress the surface structure.

To better understand the evolution of the moon’s interior and surface, Dr. Rhoden and colleagues modeled how fractures formed in Charon’s ice shell as the ocean beneath it froze.

They modeled oceans of water, ammonia or a mixture of the two based on questions about the makeup.

Advertisement

Ammonia can act as antifreeze and prolong the life of the ocean; however, results did not differ substantially.

When fractures penetrate the entire ice shell and tap the subsurface ocean, the liquid, pressurized by the increase in volume of the newly frozen ice, can be pushed through the fractures to erupt onto the surface.

Models sought to identify the conditions that could create fractures that fully penetrate Charon’s icy shell, linking its surface and subsurface water to allow ocean-sourced cryovolcanism.

However, based on current models of Charon’s interior evolution, ice shells were far too thick to be fully cracked by the stresses associated with ocean freezing.

The timing of the ocean freeze is also important. The synchronous and circular orbits of Pluto and Charon stabilized relatively early, so tidal heating only occurred during the first million years.

Advertisement

“Either Charon’s ice shell was less than 10 km (6 miles) thick when the flows occurred, as opposed to the more than 100 km (60 miles) indicated, or the surface was not in direct communication with the ocean as part of the eruptive process,” Dr. Rhoden said.

“If Charon’s ice shell had been thin enough to be fully cracked, it would imply substantially more ocean freezing than is indicated by the canyons identified on Charon’s encounter hemisphere.”

Fractures in the ice shell may be the initiation points of these canyons along the global tectonic belt of ridges that traverse the face of Charon, separating the northern and southern geological regions of the moon.

If additional large extensional features were identified on the hemisphere not imaged by NASA’s New Horizons spacecraft, or compositional analysis could prove that Charon’s cryovolcanism originated from the ocean, it would support the idea that its ocean was substantially thicker than expected.

“Ocean freezing also predicts a sequence of geologic activity, in which ocean-sourced cryovolcanism ceases before strain-created tectonism,” Dr. Rhoden said.

Advertisement

“A more detailed analysis of Charon’s geologic record could help determine whether such a scenario is viable.”

The study was published in the journal Icarus.

_____

Alyssa Rose Rhoden et al. 2023. The challenges of driving Charon’s cryovolcanism from a freezing ocean. Icarus 392: 115391; doi: 10.1016/j.icarus.2022.115391



Source link

Advertisement

Continue Reading

Space

Mimas Has an Expanding, Young Ocean, New Research Suggests | Sci.News

Published

on

By

image_4711-Mimas.jpg


Mimas, a small moon of Saturn, is heavily cratered and lacks the typical characteristics of an ocean-bearing moon, such as the active surface of Enceladus. However, measurements of Mimas, made by NASA’s Cassini mission, are best explained by an ocean under a relatively thick ice shell. In new research, a duo of planetary scientists tried to understand how this ice shell and ocean may have changed with time by modeling the formation of Mimas’ largest impact basin, Herschel.
Mimas’ heavily cratered surface suggests a cold history, but its librations rule out a homogeneous interior. Rather, Mimas must have a rocky interior and outer hydrosphere, which could include a liquid ocean or be fully frozen with a non-hydrostatic core. Image credit: NASA / JPL-Caltech / Space Science Institute.

Mimas’ heavily cratered surface suggests a cold history, but its librations rule out a homogeneous interior. Rather, Mimas must have a rocky interior and outer hydrosphere, which could include a liquid ocean or be fully frozen with a non-hydrostatic core. Image credit: NASA / JPL-Caltech / Space Science Institute.

Mimas is the innermost, and smallest (radius = 198.2 km, or 123 miles), regular moon of Saturn.

Advertisement

The moon’s surface is heavily cratered, and it is easily identified by the large Herschel impact basin.

Tectonic activity on Mimas is sparse, and there is no evidence of past or present volcanism.

“In the waning days of NASA’s Cassini mission to Saturn, the spacecraft identified a curious libration, or oscillation, in Mimas’ rotation, which often points to a geologically active body able to support an internal ocean,” said Dr. Alyssa Rhoden, a researcher at Southwest Research Institute.

“Mimas seemed like an unlikely candidate, with its icy, heavily cratered surface marked by one giant impact crater that makes the small moon look much like the Death Star from Star Wars.”

“If Mimas has an ocean, it represents a new class of small, ‘stealth’ ocean worlds with surfaces that do not betray the ocean’s existence.”

Advertisement

Dr. Rhoden and Purdue University graduate student Adeene Denton wanted to better understand how a heavily cratered moon like Mimas could possess an internal ocean.

They modeled the formation of the Hershel impact basin using iSALE-2D simulation software.

The models showed that Mimas’ ice shell had to be at least 55 km (34 miles) thick at the time of the Herschel-forming impact.

In contrast, observations of Mimas and models of its internal heating limit the present-day ice shell thickness to less than 30 km (19 miles) thick, if it currently harbors an ocean.

These results imply that a present-day ocean within Mimas must have been warming and expanding since the basin formed.

Advertisement

It is also possible that Mimas was entirely frozen both at the time of the Herschel impact and at present.

However, the authors found that including an interior ocean in impact models helped produce the shape of the basin.

“We found that Herschel could not have formed in an ice shell at the present-day thickness without obliterating the ice shell at the impact site,” said Denton, who is now a postdoctoral researcher at the University of Arizona.

“If Mimas has an ocean today, the ice shell has been thinning since the formation of Herschel, which could also explain the lack of fractures on Mimas.”

“If Mimas is an emerging ocean world, that places important constraints on the formation, evolution and habitability of all of the mid-sized moons of Saturn.”

Advertisement

“Although our results support a present-day ocean within Mimas, it is challenging to reconcile the moon’s orbital and geologic characteristics with our current understanding of its thermal-orbital evolution,” Dr. Rhoden said.

“Evaluating Mimas’ status as an ocean moon would benchmark models of its formation and evolution.”

“This would help us better understand Saturn’s rings and mid-sized moons as well as the prevalence of potentially habitable ocean moons, particularly at Uranus.”

“Mimas is a compelling target for continued investigation.”

The results were published in the journal Geophysical Research Letters.

Advertisement

_____

C.A. Denton & A.R. Rhoden. Tracking the Evolution of an Ocean Within Mimas Using the Herschel Impact Basin. Geophysical Research Letters, published online December 26, 2022; doi: 10.1029/2022GL100516



Source link

Advertisement
Continue Reading

Trending