Category: Exoplanets (page 1 of 10)

Exploring Our Sun Will Help Us Understand Habitability

The surface of the sun, with each “kernel” or “cell” roughly the size of Texas. The movie is made up of images produced by the Daniel Inouye SolarTelescope in Hawaii.  Novel and even revolutionary data and images are also expected from the Parker Solar Probe (which will travel into the sun’s atmosphere, or corona) and the just launched Solar Orbiter, which will study (among many other things) the sun’s polar regions. (NSO/NSF/AURA)

 

Scientists have been  studying our sun for centuries, and at this point know an awful lot about it — the millions of degrees Fahrenheit heat that it radiates out from the corona, the tangled and essential magnetic fields that it creates, the million-miles-per-hour solar wind and the charged high-energy solar particles that can be so damaging to anything alive.

But we have now entered a time when solar science is taking a major leap forward with the deployment of three pioneering instruments that will explore the sun and its surroundings as never before.  One is a space telescopes that will get closer to the sun (by far) than any probe before, another is a probe that will make the first observations of the sun’s poles, and the third is a ground-based solar telescope that can resolve the sun in radically new ways — as seen in the image above, released last month.

Together, NASA’s Parker Solar Probe, the joint European Space Agency-NASA Solar Orbiter mission and the National Science Foundation’s Inouye Solar Telescope on Hawai’i will provide pathways to understand some of the mysteries of the sun.  They include resolving practical issues involving the dynamics  of “space weather” that can harm astronauts and telecommunications systems, and larger theoretical unknowns related to all the material that stars scatter into space and onto planets.

Some of those unresolved questions include determining how and why heat and energy flow from the sun’s inner core to the outer corona and make it so much hotter, determining the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind, the make-up and effects of solar flares and coronal mass ejections, and how and why the sun is able to create and control the heliosphere — the vast bubble of charged particles blown by the solar wind into interstellar space.

 

An illustration of Kepler2-33b, , one of the youngest exoplanets detected to date using NASA Kepler Space Telescope.

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

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

Tatooine Worlds

Science fiction has become science.  No habitable planets orbiting two suns like the fictional Tatooine have been detected so far, but more than a dozen “circumbinary planets” have been identified and many more are predicted.  Exoplanets orbiting a host star that orbits its own companion star are even more common. (Lucasfilm)

When the the first Star Wars movie came out in 1977, it featured the now-iconic two-sun, “circumbinary” planet Tatooine.  At that time astronomers didn’t really know if such solar systems existed, with more than one sun and at least one planet.

Indeed, the first extra-solar planet wasn’t detected until the early 1990s.  And the first actual circumbinary planet was detected in 2005, and it was a Jupiter-size planet orbiting a system composed of a sun-like star and a brown dwarf.  Tatooine was definitely not a Jupiter-size planet.

But since then, the presence and distribution of circumbinaries has grown to a dozen and some the planets discovered orbiting the two stars have been smaller.  The most recent discovery was announced this week and was made using the Transiting Exoplanet Survey Satellite (TESS) space telescope

The new planet, called TOI (TESS Object of Interest)-1338 b, is about 6.9 times larger than Earth. It orbits its pair of host stars every 95 days, while the stars themselves orbit each other in 15 days.

As is common with binary stars, one is more massive and much brighter than the other (5976 K and 3657 K, respectively, with our sun at  5780 K),  and as the planet orbits around it blocks some of the light from the brighter star.

This transit allows astronomers to measure the size of the planet.  The transit — as scientific luck, or skill, would have it — was first found in the TESS data by a high school student working at NASA with over the summer,  Wolf Cukier

“I was looking through the data for everything the volunteers had flagged as an eclipsing binary, a system where two stars circle around each other and from our view eclipse each other every orbit,” Cukier said. “About three days into my internship, I saw a signal from a system called TOI 1338.”

“At first I thought it was a stellar eclipse, but the timing was wrong. It turned out to be a planet.”

With all of the data available from observations past and current, planet hunting clearly isn’t the scientific Wild West that it used to be — although the results remain often eye-popping and surprising.… Read more

A Southern Sky Extravaganza From TESS

Candidate exoplanets as seen by TESS in a southern sky mosaic from 13 observing sectors. (NASA/MIT/TESS)

NASA’s Transiting Exoplanet Survey Satellite (TESS) has finished its one year full-sky observation of  Southern sky and has found hundreds of candidate exoplanets and 29 confirmed planets.  It is now maneuvering  its array of wide-field telescopes and cameras to focus on the northern sky to do the same kind of exploration.

At this turning point, NASA and the Massachusetts Institute of Technology — which played a major role in designing and now operating the mission — have put together mosaic images from the first year’s observations, and they are quite something.

Constructed from 208 TESS images taken during the mission’s first year of science operations, these images are a unique  space-based look at the entire Southern sky — including the Milky Way seen edgewise, the Large and Small Magellenic galaxies, and other large stars already known to have exoplanet.

“Analysis of TESS data focuses on individual stars and planets one at a time, but I wanted to step back and highlight everything at once, really emphasizing the spectacular view TESS gives us of the entire sky,” said Ethan Kruse, a NASA Postdoctoral Program Fellow who assembled the mosaic at NASA’s Goddard Space Flight Center.

Overlaying the figures of selected constellations helps clarify the scale of the TESS southern mosaic. TESS has discovered 29 exoplanets, or worlds beyond our solar system, and more than 1,000 candidate planets astronomers are now investigating. NASA/MIT/TESS

The mission is designed to vastly increase the number of known exoplanets, which are now theorized to orbit all — or most — stars in the sky.

TESS searches for  the nearest and brightest main sequence stars hosting transiting exoplanets, which are the most favorable targets for detailed investigations.

This animation shows how a dip in the observed brightness of a star may indicate the presence of a planet passing in front of it, an occurrence known as a transit. This is how TESS identified planet.
(NASA’s Goddard Space Flight Center)

While previous sky surveys with ground-based telescopes have mainly detected giant exoplanets, TESS will find many small planets around the nearest stars in the sky.  The mission will also provide prime targets for further characterization by the James Webb Space Telescope, as well as other large ground-based and space-based telescopes of the future.

The TESS observatory uses an array of wide-field cameras to perform a survey of 85% of the sky.… Read more

A Telling Nobel Exoplanet Faux Pas

This is the Doppler velocity curve displayed by the Nobel Committee to illustrate what Mayor and Queloz had accomplished in 1995. But actually, the graph shows the curve from the Lick Observatory in California that an American team had produced to confirm the initial finding. Such was the interweaving of the work of the Swiss and the American teams searching for the first exoplanet orbiting a sun-like star. (Image courtesy of Geoff Marcy and Paul Butler, San Francisco State University)

Given the complex history of the discovery and announcement in 1995 of the first exoplanet that orbits a sun-like star, it is perhaps no surprise that errors might sneak into the retelling.  Two main groups were racing to be first, and for a variety of reasons the discovery ended up being confirmed before it was formally announced.

A confusing situation prone to mistakes if all involved aren’t entirely conversant with the details.  But an error — tantamount to scientific plagiarism — by the Nobel Committee?   That is a surprise.

The faux pas occurred at the announcement on October 8 that Michel Mayor of the University of Geneva and Didier Queloz of the the University of Cambridge had won the Nobel for physics to honor their work in detecting that first exoplanet orbiting a sun-like star.

As Nobel Committee member Ulf Danielsson described the achievement, a powerpoint display of important moments and scientific findings in their quest was displayed on a screen behind him.

When the ultimate image was on deck to be shown  — an image that presented the Doppler velocity curve that was described as the key to the discovery — the speaker appeared to hesitate after looking down to see what was coming next.

If he did hesitate, it was perhaps because to those in the know, the curve did not come from Mayor and Queloz.

Rather, it was the work of a team led by Geoffrey Marcy and Paul Butler — the San Francisco State University group that confirmed the existence of the hot Jupiter exoplanet 51 Pegasi b several days after the discovery was made public (to some considerable controversy) at a stellar systems conference in Florence.  So at a most significant juncture of the Nobel introduction of the great work of Mayor and Queloz, hard-won data by a different team was presented as part of the duo’s achievement.

This is both awkward and embarrassing, but it also indirectly points to one of the realities that the Nobel Committee is forced, by the will of Alfred Nobel, to ignore:  That science is seldom the work now of but two or three people.… Read more

The Remarkable Race to Find the First Exoplanet, And the Nobel Prize It Produced

Rendering of the planet that started it all — 51 Pegasi b. It is a “hot Jupiter” that, when discovered, broke every astronomical rule regarding where types of planets should be in a solar system. (NASA)

Earlier this week, the two men who detected the first planet outside our solar system that circled a sun-like star won a Nobel Prize in physics.  The discovery heralded the beginning of the exoplanet era — replacing a centuries-old scientific supposition that planets orbited other stars with scientific fact.

The two men are Michel Mayor,  Professor Emeritus at the University of Geneva and Didier Queloz, now of Cambridge University.  There is no Nobel Prize in astronomy and the physics prize has seldom gone to advances in the general field of astronomy and planetary science.  So the selection is all the more impressive.

Mayor and Queloz worked largely unknown as they tried to make their breakthrough, in part because previous efforts to detect exoplanets (planets outside our solar system) orbiting sun-like stars had fallen short, and also because several claimed successes turned out to be unfounded.  Other efforts proved to be quite dangerous:  a Canadian duo used poisonous and corrosive hydrogen flouride vapor in the 1980s as part of their planet-hunting effort.

But since their 1995 discovery opened the floodgates, the field of exoplanet science has exploded.  More than 4,000 exoplanets have been identified and a week seldom goes by without more being announced.  The consensus scientific view is now that billions upon billions of exoplanets exist in our galaxy alone.

While Mayor and Queloz were pioneers for sure, they did not work in a vacuum.  Rather, they were in a race of sorts with an American team that had also been working in similar near anonymity for years to also find an exoplanet.

And so here is a human, rather than a purely scientific, narrative look — reported over the years — into the backdrop to the just announced Nobel Prize.  While Mayor and Queloz were definitely the first to find an exoplanet, they were quite close to being the second.

 

Swiss astronomers Didier Queloz and Michel Mayor are seen here in 2011 in front of the European Southern Observatory’s ’s 3.6-metre telescope at La Silla Observatory in Chile. The telescope hosts the High Accuracy Radial Velocity Planet Searcher (HARPS), one of the world’s leading exoplanet hunters.  After the discovery of 51 Pegasi b, Mayor led the effort to build the HARPS planet-finding spectrometer.

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The Giant Moon That Might Be the Heart of a Jupiter

Artist’s impression of the exomoon candidate Kepler-1625b-i, the planet it is orbiting and the star. (NASA/ESA/L. Hustak, STScI)

“Moons are where planets were in the 1990s,” predicted René Heller from the Max Planck Institute for Solar System Research a few years ago. “We’re on the brink.”

Heller was predicting that we were close to the first discoveries of exomoons: moons that orbit extrasolar planets outside our solar system. When a possible exomoon detection was announced in 2017, Heller’s prediction was proved correct. Not only had we found a candidate moon, but its properties defied our formation theories just as with the discoveries of the first exoplanets.

However, a paper published in Science this month has proposed a method for building this most unusual of moons.

As we move away from the sun, the planets of our solar system become mobbed with moons. How these small worlds formed is attributed to three different processes:

Moons in our solar system are thought to have formed through three different mechanisms (E. Tasker / Many Worlds)

The most extensive moon real estate orbits our gas giants, Jupiter, Saturn, Uranus and Neptune. The majority of these moons are thought to have been born during the planets’ own formation, forming in disks of gas, dust and ice that circled the young worlds. These circumplanetary disks are like miniaturised versions of the protoplanetary disks that circle young stars and give rise to planets.

One exception to this is Neptune’s moon, Triton, which orbits in the opposite direction to the planet’s rotation. This retrograde path would not be expected to arise if Triton has formed out of a circumplanetary disk around Neptune, which always rotate the same direction as the forming planet. Instead, Triton was likely a dwarf planet that was snagged by Neptune’s gravity during a chance encounter.

The capture scenario has also been proposed for the two moons of Mars. The lumpy satellites resemble asteroids and may have been born in the asteroid belt that sits between Mars and Jupiter. However, both moons orbit the red planet in circular orbits that sit in the same plane, pointing to a more disk-like formation method. Although Mars is too small to have had a substantial circumplanetary disk during formation, a giant impact later in its history could have thrown debris into orbit. This debris disk could then have coalesced into the two moons.

Such a violent start to Mars’s moons would mimic the beginnings of our own moon.… Read more

The Planets Too Big for Their Star

Artist rendering of a red dwarf , with three exoplanets orbiting. About 75% of all stars in the sky are the cooler, smaller red dwarfs. (NASA)

Two giant planets have been found orbiting a tiny star, defying our theories for how planets are formed.

To be entirely truthful, there is nothing new in an exoplanet discovery shredding our current ideas about how planets are built. The first extrasolar planets ever discovered orbit a dead star known as a pulsar. Pulsars end their regular starry life in a colossal supernova explosion that should incinerate or eject any orbiting worlds. This discovery was followed a few years later by the first detection of a hot Jupiter; a gas giant planet orbiting its star in just a few days, defying theories that said such planets should form on long orbits where there is more building material to make massive worlds. Exoplanet hunting is a field full of surprises and now, it has one more.

GJ 3512 is a red dwarf star with a luminosity only around a thousandth (0.0016L) of our sun. The small size of these stars makes it easier to detect the presence of a planet, and many of our most famous exoplanet discoveries have been found orbiting red dwarf stars, including Proxima Centauri b and the seven worlds in the TRAPPIST-1 system. But a notable attribute of these systems is that the planets are small. Unlike our own sun which boasts four gas giant worlds, planets around red dwarfs are typically smaller than Neptune.

Artist impression of the seven planets of Trappist-1 that also orbit a red dwarf star. These are small worlds. Jupiter-sized gas giants were not previously thought to form around the small red dwarf stars (NASA/JPL-Caltech).

This preference for downsized worlds is assumed to be due to the protoplanetary disk; the disk of dust and gas that swirls around young stars out of which planets are born. Protoplanetary disks around small stars tend to be low mass and puffy. This limits and spreads out the solid material, making it difficult for a young planet to grow.

Yet the two planets discovered around GJ 3512 are not small.
Led by Juan Carlos Morales at the IEEC Institute of Space Studies of Catalonia, the announcement of the discovery was published in the journal Science today.

The team detected these two new worlds using the radial velocity technique which measures the wobble in the position of the star due to the gravitational tug of the orbiting planet.… Read more

Searching for the Edge of Habitability

Topographical map of Venus by NASA’s Magellan spacecraft (1990 – 1994). Color indicates height. (NASA/JPL/USGS)

How many habitable worlds like our own could exist around other stars? Since the discovery of the first exoplanets, the answer to this question has seemed tantalizingly close. But to estimate the number of Earths, we first need to understand how our planet could have gone catastrophically awry.

In other words, we need to return to Venus.

We have now discovered over 4000 planets beyond our solar system. Approximately one-third of these worlds are Earth-sized and likely to have rocky surfaces not crushed under deep atmospheres. The next step is to discover how many of these support temperate landscapes versus ones unsuitable for life.

The Earth’s habitability is often ascribed to the level of sunlight we receive. We orbit in the so-called ‘habitable zone’ where our planet’s geological cycle can adjust the level of carbon dioxide in our atmosphere to keep our seas liquid. In a closer orbit to the sun, this cycle could not operate fast enough to keep the Earth cool. Our seas would evaporate and our atmosphere fill with carbon dioxide, sending the planet temperature into an upwards spiral known as a runaway greenhouse.

If our solar system had just one Earth-sized planet, this would suggest we could simply count-up similar sized planets in the habitable zones around other stars. This would then be our set of the most likely habitable worlds.

However, this idea is shredded in a new paper posted this month to be published in the Journal of Geophysical Research: Planets. Led by Stephen Kane from the University of California, Riverside, the paper is authored by many of the top planetary scientists we have met before in this column.

Their message is simple: our sun is orbited by two Earth-sized planets but only one is habitable. To identify habitable planets around other stars, we need to explain why the Earth and Venus evolved so differently. And the data suggests this is not just a climate catastrophe.

Orbiting beyond the inner edge of the habitable zone, Venus does appear at first to be a runaway Earth. The planet’s atmosphere is 96.5% carbon dioxide, smothering the surface to escalate temperatures to a staggering 863°F (462°C). Images from NASA’s Pioneer Venus mission in the late 1970s revealed a surface of highlands and lowlands that resembled the continents of Earth. This is all consistent with a picture of an Earth-like planet with a runaway greenhouse atmosphere.… Read more

“Agnostic Biosignatures,” And the Path to Life as We Don’t Know It

Most research into signs of life in our solar system or on distant planets uses life on Earth as a starting point. But now NASA has begun a major project to explore the potential signs of life very different from what we have on Earth.  For example, groups of molecules, like those above, can be analyzed for complexity, regardless of their specific chemical constituents.  ( Brittany Klein/Goddard Space Flight Center)

Biosignatures – evidence that says or suggests that life has been present – are often very hard to find and interpret.

Scientists examining fossilized life on Earth can generally reach some sort of agreement about what is before them, but what about the soft-bodied or even single-celled organisms that were the sum total of life on Earth for much of the planet’s history as a living domain? Scientific disagreements are common.

Now think of trying to determine whether a particular outline on an ancient Martian rock, or a geochemical or surface anomaly on that rock, is a sign of life. Or perhaps an unexpected abundance of a particular compound in one of the water vapor plumes coming out of the moons Europa or Enceladus. Or a peculiar chemical imbalance in the atmosphere of a distant exoplanet as measured in the spectral signature collected via telescope.

These are long-standing issues and challenges, but they have taken on a greater urgency of late as NASA missions  (and those of other space agencies around the world) are being designed to actively look for signs of extraterrestrial life – most likely very simple life – past or present.

And that combination of increased urgency and great difficulty has given rise to at least one new way of thinking about those potential signs of life. Scientists call them “agnostic biosignatures” and they do not presuppose any particular biochemistry.

“The more we explore the solar system and distant exoplanets, the more we find worlds that are really foreign,”  said Sarah Stewart Johnson, at an assistant professor at Georgetown University and principal investigator of the newly-formed Laboratory for Agnostic Biosignatures (LAB).  The LAB team won a five-year, $7 million grant last year from NASA’s Astrobiology Program.

“So our goal is to go beyond our current understandings and find ways to explore the world of life as we don’t know it,” she told me.  “That might mean thinking about a spectrum of how ‘alive’ something might be… And we’re embracing uncertainty, looking as much for biohints as biosignatures.”… Read more

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