What a Menagerie

Category: What a Menagerie (page 1 of 5)

Why Does Our Solar System Have No Super-Earths, and Other Questions for Comparative Planetology

An artist’s impression of the exoplanet LHS 1140b, which orbits a red dwarf star 40 light-years from Earth. Using the European Southern Observatory’s telescope at La Silla, Chile, and other telescopes around the world, an international team of astronomers discovered this super-Earth orbiting in the habitable zone around the faint star LHS 1140. This world is a little larger and much more massive than the Earth. (ESO)

Before the explosion in discovery of extrasolar planets, the field of comparative planetology was pretty limited — confined to examining the differences between planets in our solar system and how they may have come to pass.

But over the past quarter century, comparative planetology and the demographics of planets came to mean something quite different. With so many planets now identified in so many solar systems, the comparisons became not just between one planet and another but also between one solar system and another.

And the big questions for scientists became the likes of: How and why are the planetary makeups of distant solar systems often so different from our own and from each other; what does the presence or absence of large planets in a solar system do to the distribution of smaller planets; how large can a rocky planet can get before it turns to a gas giant planet; and on a more specific subject, why do some solar systems have hot Jupiters close to the host star and others have cold Jupiters much further out like our own

Another especially compelling question involves our own solar system, though as something of an outlier rather than a prototype.

That question involves the absence in our solar system of anything in the category of a “super-Earth” — a rocky or gaseous extrasolar planet with a mass greater than Earth’s but substantially below those of our solar system’s planets next in mass, Uranus and Neptune.

The term “super-Earth” refers only to the mass and radii of the planet, and so does not imply anything about the surface conditions or habitability. But in the world of comparative planetology “super-Earths” are very important because they are among the most common sized exoplanets found so far and some do seem to have planetary characteristics associated with habitability.

Yet they do not exist in our solar system. Why is that?

Artist rendition of Earth in comparison to one of the many super-Earth planets. (NASA)

In a recent article in The Astrophysical Journal Letters, planetary demographer Gijs D.… Read more

Introducing Hycean Planets

August 31, 2021 / Marc Kaufman / 0 Comments

A so-called Hycean planet is one featuring large oceans and a hydrogen atmosphere. A new report from the University of Cambridge suggests this kind of planet, sized between a super-Earth and a mini-Neptunes, could potentially support life. The image features a red dwarf star as the planet’s host star. (Artist rendering by Amanda Smith, University of Cambridge)

Planets beyond our solar system, we now know, come in all shapes, sizes and consistencies. There are rocky planets, water worlds, gaseous planets, super-Earths, hot Jupiters, tidally locked planets, planets in orbital resonance with each other, and so much more.

A group of exoplanet researchers at the University of Cambridge have recently proposed a new category of planet, one that has seldom been considered even potentially habitable. They call them Hycean planets due to the presence of substantial hydrogen in the atmospheres and large oceans (hydrogen and ocean = Hycean) on their surfaces.

And in an article in The Astrophysical Journal, they make the case that under certain conditions, some Hycean planets could, indeed, be habitable.

“Hycean planets open a whole new avenue in our search for life elsewhere,” said Nikku Madhusudhan from Cambridge’s Institute of Astronomy, who led the research.

Many of the prime Hycean candidates identified by the researchers are bigger and hotter than Earth, but the researchers argue that they still have the characteristics to host large oceans that could support microbial life similar to that found in some of Earth’s most extreme watery environments.

Hycean planets, Madhusudhan said in a release, offer a new paradigm for the search for life beyond Earth.

“Essentially, when we’ve been looking for these various molecular signatures, we have been focusing on planets similar to Earth, which is a reasonable place to start,” he said. “But we think Hycean planets offer a better chance of finding several trace biosignatures.”

Co-author Anjali Piette, also from Cambridge, added: “It’s exciting that habitable conditions could exist on planets so different from Earth.”

An artist rendering of what a possible Hycean planet would look like. This image is of K2-18b, which has a radius twice that of Earth and is more than eight times as massive as our planet. The heavy hydrogen atmosphere is present, as is the red dwarf star that it orbits. (Alex Boersma)

There are no planets of this size and type in our solar system, but planets in the Hycean range are quite common in the galaxy.… Read more

A Young Planet Found That May Well Be Making Moons

July 27, 2021 / Marc Kaufman / 0 Comments

An image made by the Very Large Telescope in Chile shows a forming planet, the bright spot at right. The overpowering light of the host star is blocked out by a coronagraph inside the telescope. (ESO/A. Müller et al.)

Astronomers have many theories about how planets are formed within the gas, dust, pebbles and gradually rocks of the circumstellar disks that encircle a star after it has been born. While the general outlines of this remarkable process are pretty well established, many questions large and small remain unanswered.

One is how and when exomoons are formed around these planets, with the assumption that the process that forms planets must also give birth moons. But the potential moons have been far too small for the current generation of space and ground telescopes to identify.

Now astronomers have detected something almost as significant: a circumplanetary disk surrounding a young planet that appears to be in the process of making moons. The moon itself has not been detected, but a forming planet has been found with a ring of dust and gas that surrounds it. And within that circumplanetary disk, astronomers infer, a moon is possibly being formed.

“Our work presents a clear detection of a disk in which satellites could be forming,” said Dr. Myriam Benisty, an astronomer at the University of Grenoble and the University of Chile.

“The new … observations were obtained at such exquisite resolution that we could clearly identify that the disk is associated with {the exoplanet} and we are able to constrain its size for the first time,” she said in a release.

While the first detection of the planet was made via the European Southern Observatory’s Very Large Telescope in Chile, the more granular observation of the forming planet and its moon-forming disk was made with the Atacama Large Millimeter/submillimeter Array (ALMA), also in Chile.

This ALMA image shows the young PDS 70 planetary system. The system features a star at its center and at least two planets orbiting it, PDS 70b (not visible in the image) and PDS 70c, surrounded by a circumplanetary disk (the dot to the right of the star). Image credit: ALMA / ESO / NAOJ / NRAO / Benisty et al.)

The finding, published in the Astrophysical Journal Letters, came via direct imaging — in effect through extremely high power photography rather through the indirect methods much more common in exoplanet astronomy.… Read more

A Close Exoplanet Found That May Have An Atmosphere Ideal For Study

March 4, 2021 / Marc Kaufman / 1 Comment

Planet Gliese 486b is close to us (in a relative sense), rocky, on the small side and may have an atmosphere. These conclusions come from studying the planet using both the transit and radial velocity techniques, which have been the primary methods used by astronomers to find and characterize exoplanets. Charts showing the presence of the planet using both techniques are in the blue boxes. (Render Area, Max Planck Institute for Astronomy, MPIA)

Different methods of searching for and finding distant exoplanets give different information about the planets found.

The transit method — where an exoplanets passed in front of its sun and dims the bright sunlight ever so slightly — gives astronomers not only a detection but also its radius or size.

The radial velocity method — where an exoplanet’s gravity causes its host star to “wobble” in a way that can be measured — provides different information about mass and orbit.

If a planet can be measured by both the transit and radial velocity methods, an important added dimension can be determined — how dense the planet might be. This tells us if the planet is rocky or gaseous, watery or even if it has a central core and might have an atmosphere. So many things have to go right that this kind of dual detection has seldom been accomplished for a relatively small and rocky planet, but such a new planet has now been found.

The planet, Gliese 486b, is a super-Earth orbiting its host star at only 24 light-years away. That makes the planet the third closest transiting exoplanet to Earth that is known, and the closest with a measured mass that transits a red dwarf star.

The authors of the study in the journal Science say Gliese 486b is an ideal candidate for learning how to best search for and characterize an all-important atmosphere, and to study potential habitability, too. Future telescopes will make this kind of work more of a reality.

“Gliese 486 b is not hot enough to be a lava world,” lead author Trifon Trifonov of the Max-Planck-Institut für Astronomie and colleagues write. “But its temperature of ~700 Kelvin (800 degrees Fahrenheit) makes it suitable for emission spectroscopy and …. studies in search of an atmosphere.”

Artist impression of the surface of the newly discovered hot super-Earth Gliese 486 b. With a temperature of about 700 Kelvin (almost 800 degrees Fahrenheit), 486b possibly has an atmosphere.

More Weird and Wild Planets

January 13, 2021 / Marc Kaufman / 0 Comments

A world called TOI-849b could be the exposed, naked core of a former gas giant planet whose atmosphere was blasted away by its star. Every day is a bad day on planet TOI-849b. . It hugs its star so tightly that a year – one trip around the star – takes less than a day. And it pays a high price for this close embrace: an estimated surface temperature of nearly 2,800 degrees Fahrenheit (1,500 degrees Celsius) It’s a scorcher even compared to Venus, which is 880 degrees Fahrenheit (471 degrees Celsius). About half the mass of our own Saturn, this planet orbits a Sun-like star more than 700 light-years from Earth. (NASA/Exoplanet Exploration Program)

The more we learn about the billions upon billions of planets that orbit beyond our solar system, the more we are surprised by the wild menagerie of objects out there. From the start, many of these untolled planets have been startling, paradigm-breaking, mysterious, hellish, potentially habitable and just plain weird. Despite the confirmed detection of more than 4,000 exoplanets, the job of finding and characterizing these worlds remains in its early phases. You could make the argument that learning a lot more about these distant exoplanets and their solar systems is not just one of the great tasks of future astronomy, but of future science.

And that is why Many Worlds is returning to the subject of “Weird Planets,” which first appeared in this column at the opening of 2019. It has been the most viewed column in our archive, and a day seldom goes by without someone — or some many people — decide to read it.

So here is not a really a sequel, but rather a continuation of writing about this unendingly rich subject. And as I will describe further on, almost all of the planets on display so far have been detected and characterized without ever having been seen. The characteristics and colors presented in these (mostly) artistic renderings are the result of indirect observing and discovery — measuring how much light dims when a faraway planet crosses its host star, or how much the planet’s gravity causes its sun to move.

As a result, these planets are sometimes called “small, black shadows.” Scientists can infer a lot from the indirect measurements they make and from the beginnings of the grand effort to spectroscopically read the chemical makeup of exoplanet atmospheres. … Read more

Sparkling Gifts From the Hubble Space Telescope, Thirty Years Into Its Mission

December 21, 2020 / Marc Kaufman / 0 Comments

This Hubble image captures globular star cluster (NGC 6541) that is roughly 22,000 light-years from Earth. A globular cluster is a spherical collection of stars that orbits a galactic core. They are very tightly bound by gravity, which gives them their spherical shapes,and relatively high density of stars toward their centers. The cluster is bright enough that backyard stargazers in the Southern Hemisphere can spot it with binoculars, though certainly not in this detail. (NASA, ESA, and G. Piotto (Università degli Studi di Padova)

For almost 30 years now, the Hubble Space Telescope has transformed how we see the cosmos. In terms of scientific output as well as making visible the splendors of the sky above us, the Hubble has been arguably the most consequential telescope ever to peer into space.

To commemorate 30 years of Hubble science and images, NASA and the European Space Agency have released 30 previously unpublished images of galaxies, star clusters and nebula from what is known as the Caldwell catalogue, a collection compiled by British amateur astronomer and science communicator Sir Patrick Caldwell-Moore.

These images have been taken by Hubble throughout its time in space and used for scientific research or for engineering tests, but NASA had not fully processed the images for public release until now.

At the end of a difficult year, they offer the glitter, the grandeur and the cosmic marvel that the Hubble provides so well and that perhaps people could use right now.

This Hubble image captures a small region on the edge of the inky Coalsack Nebula. A nebula is an enormous cloud of dust and gas occupying the space between stars and acting as a nursery for new stars. Coalsack is a “dark nebula” which completely blocks out visible wavelengths of light from objects behind it. The image was made using Hubble’s Advanced Camera for Surveys in both visible and infrared wavelengths. (NASA, ESA, and R. Sahai of NASA’s Jet Propulsion Laboratory)

The Hubble famously entered into Earth orbit and began its mission with the calamitous discovery of a near-fatal mistake — the main mirror had been ground incorrectly and could not accomplish much viewing. The telescope was about 340 miles from Earth and never before had NASA undertaken a mission to repair a spacecraft that far away.

But in 1993 seven astronauts flew to the Hubble on the space shuttle Endeavour, spent five days repairing it and the rest is history. … Read more

Cores, Planets and The Mission to Psyche

August 20, 2020 / Marc Kaufman / 0 Comments

The asteroid Psyche will be the first metal-rich celestial body to be visited by a spacecraft. The NASA mission launches in 2022 and is expected to arrive at the asteroid in late 2026. A central question to be answered is whether Psyche is the exposed core of a protoplanet that was stripped of its rocky mantle. (NASA)

Deep inside the rocky planets of our solar system, as well as some solar system moons, is an iron-based core.

Some, such as Earth’s core, have an inner solid phase and outer molten phase, but the solar system cores studied so far are of significantly varied sizes and contain a pretty wide variety of elements alongside the iron. Mercury, for instance, is 85 percent core by volume and made up largely of iron, while our moon’s core is thought to be 20 percent of its volume and is mostly iron with some sulfur and nickel.

Iron cores like our own play a central role in creating a magnetic field around the planet, which in turn holds in the atmosphere and may well be essential to make a planet habitable. They are also key to understanding how planets form after a star is forged and remaining dense gases and dust are kicked out to form a protoplanetary disk, where planets are assembled.

So cores are central to planetary science, and yet they are obviously hard to study. The Earth’s core starts about 1,800 miles below the surface, and the cores of gas giants such as Jupiter are much further inward, and even their elemental makeups are not fully understood.

All this helps explains why the upcoming NASA mission to the asteroid Psyche is being eagerly anticipated, especially by scientists who focus on planetary formation.

Scheduled to launch in 2022, the spacecraft will travel to the main asteroid belt between Mars and Jupiter and home in on what has been described as an unusual “metal body,” which is also one of the largest asteroids orbiting the sun.

While some uncertainty remains, it appears that Psyche is the exposed nickel-iron core of a long-ago emerging rocky protoplanet, with the rest of the planet stripped away by collisions billions of years ago.

An artist’s impression of solar system formation, and the formation of a protoplanetary disk filled with gases and dust that over time clump together and smash into each other to form larger and larger bodies. (Gemini Observatory/AURA artwork by Lynette Cook )

That makes Psyche a most interesting place to visit.… Read more

How Many Habitable Zone Planets Can Orbit a Host Star?

August 10, 2020 / Marc Kaufman / 0 Comments

This representation of the Trappist-1 system shows which planets could potentially have temperature conditions which would allow for the presence of liquid water, seen generally as essential for life. The inner three planets are likely too hot, and the outer planet is probably too cold, but the middle three planets might be just right. (NASA / JPL-Caltech)

Our solar system has but one planet orbiting in what is commonly known as the habitable zone — at a distance from the host star where water could be liquid at times rather than always ice or gas. That planet, of course, is Earth.

But from a theoretical, dynamical perspective, does this always have to be the case? The answer to that question is no because a number of stars are known to have more than one habitable zone planet.

Now a team from the University of California, Riverside has produced a study that concludes as many as seven Earth-sized, habitable zone planets could orbit a single star — if there were no large Jupiter-sized planets in the system and if the star was of a particular type.

The article, published in the Astronomical Journal, concluded that seven habitable zone planets was the maximum for a star, but a sun such as ours could potentially support six planets with sometimes liquid water — a condition considered essential for life.

Study leader Stephen Kane, an astrobiologist who focuses on potentially habitable exoplanets, said he had been studying the nearby solar system Trappist-1, which has three Earth-like planets in its habitable zone and seven planets all together.

“This made me wonder about the maximum number of habitable planets it’s possible for a star to have, and why our star only has one,” Kane said.

With the discovery of an eighth planet, the Kepler-90 system is the first to tie with our solar system in number of planets. Artist’s concept. Credit: NASA/Ames Research Center/Wendy Stenzel

His conclusion:

“Even though (our solar system) only has one planet in the habitable zone, it’s not necessarily the typical situation. A far more typical scenario may be to have many planets in the habitable zone, depending on the presence of a giant planet.”

More later about the destabilizing effects of giant planet, but the Kane (and others) say that looking for solar systems without Jupiter-size planets has become increasingly important because of this effect on other terrestrial planets.

To determine how many habitable zone planets might be possible in a solar system, his team created a model system in which they simulated planets of various sizes orbiting their stars.

Thinking About Life (or Lyfe) Through The Prism of “Star Trek”

June 17, 2020 / Guest Author / 1 Comment

This column was written for Many Worlds by Michael L. Wong and Stuart Bartlett. Wong is a postdoctoral research associate at the University of Washington’s Astronomy and Astrobiology program and is a member of NASA’s Nexus for Exoplanet System Science (NExSS) initiative as part of the university’s Virtual Planetary Laboratory team. Bartlett is a postdoctoral scholar in Geochemistry at the California Institute of Technology and has been a fellow at the Earth-Live Science Institute (ELSI) in Tokyo.

Spock communicates with a Horta, a fictional silicon-based life form composed of molten rock and acid. (Star Trek; CBS Studios)

By Michael L. Wong and Stuart Bartlett

The search for extraterrestrial life is in its early phase still and, the truth is, we don’t yet know if life exists beyond our pale blue dot. Or, if it does, whether it will be easily recognizable or truly bizarre.

Predicting what might be out there, and how to find it, is a hypothesis-driven area of research at present — one that has given rise to hundreds of possible definitions for the “life” we are looking for.

But after grounding ourselves in scientific principles, it may be that our greatest tool is to let our imaginations fly. Science fiction often helps us embrace our ignorance of what might be out there.

In the Star Trek universe, our galaxy is teeming with life—both astonishingly familiar and incredibly different.

The familiar variety includes Mr. Spock, the U.S.S. Enterprise’s half-human, half-Vulcan science officer. He is the product of an extraordinary cosmic coincidence: the emergence of nearly identical biochemical machinery on two completely separate worlds. Vulcans—despite their pointy ears, upswept eyebrows, and a nearly religious devotion to bowl cuts—are incredibly similar to humans on the cellular, genetic, and metabolic level.

We can share meals, share air, and, yes, share intimacy. Even their green, copper-based blood is not as alien as it might seem; this trait is typical of most mollusks and crustaceans on Earth.

The Crystalline entity was a powerful, spaceborne creature characterized by a crystalline structure that resembled a large snowflake. (Star Trek; CBS Studios)

But Star Trek also depicts life forms that are incredibly dissimilar from you, me, or Mr. Spock.

Take the Horta, for example. This lumpy mass, like a misshapen meatball crossed with a child’s volcano science experiment, is a silicon-based life form composed of molten rock and acid.

Then there’s Q, a non-corporeal being that possesses god-like powers which, it seems, are directed solely upon harassing Captain Jean-Luc Picard.… Read more

Exactly How Like Our Earth is an Earth-like Planet?

January 28, 2020 / Elizabeth Tasker / 0 Comments

Explainer video for Earth-Like. (Vimeo edition with subtitles here)

Are we alone? The question hangs over each discovery of an Earth-sized planet as we speculate on its habitability. But how different and varied could these worlds really be? Perhaps the best way to get a flavor of this potential diversity is to build a few planets.

This is the idea behind Earth-Like: a website and twitter bot that lets you build your own Earth-like world. Earth-Like begins with a planet that resembles our Earth today, with oceans flowing over the surface and an atmosphere that maintains the global average temperature at a comfortable 15°C (59°F) on our orbit within the habitable zone. By making changes to the fraction of exposed land, the volcanic rate and position within the habitable zone, you can change the conditions on our planet into wildly different environments from desert to snowball.

Earth-Like can create a visualisation of what your planet might look like. This one is 91% covered with land, sitting in the middle of the habitable zone with 5 x the volcanic rate of Earth today! Its average temperature is about 9°C (48°F).

The concept for Earth-Like began during a workshop on planet diversity held at the Earth-Life Sciences Institute (ELSI) in Tokyo. The discussions highlighted that the potential for variation between rocky worlds is vast. A planet rich in carbon could have a mantle of diamond. A stagnant surface rather than mobile continental plates could throttle volcanism. The gravity on a large rocky planet might flatten the topology to allow shallow seas to cover all the land.

At the moment, observations can only tell us the physical size (either radius or mass) and the orbit of the majority of extrasolar planets. As we do not know what the surface of these worlds is like, we dub new discoveries Earth-like or potentially habitable if their size and the amount of radiation they receive from the star is similar to Earth. But this fails to convey how incredibly alien these worlds could be.

Earth-Like was spearheaded by undergraduate student, Kana Ishimaru, at the University of Tokyo (now a graduate student at the University of Arizona), working with myself, Julien Foriel (now a researcher at Harvard University) and Nicholas Guttenberg at ELSI. We wanted to build a model that would give a feel of the diversity of potentially habitable worlds and which could be run easily on a web browser.… Read more

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