Category: Planetary Systems (page 1 of 9)

Mapping Titan, the Most Earth-Like Body in Our Solar System

In an image created by NASA’s Cassini spacecraft, sunlight reflects off lakes of liquid methane around Titan’s north pole.  Cassini radar and visible-light images allowed researchers to put together the first global geological map of Saturn’s largest moon.  (NASA/JPL-Caltech/University of Arizona/University of Idaho)

Saturn’s moon Titan has lakes and rivers of liquid hydrocarbons, temperatures that hover around -300 degrees Fahrenheit, and a thick haze that surrounds it and has cloaked it in mystery.   An unusual place for sure, but perhaps what’s most unusual is that Titan more closely resembles Earth of all the planets and moons in our solar system.

This is because like only Earth it has that flowing liquid on its surface, it has a climate featuring wind and rain that form dunes, rivers, lakes, deltas and seas (probably of filled with liquid methane and ethane), it has a thick atmosphere and it has weather patterns that change with the seasons.  The moon’s methane cycle is quite similar to our water cycle.

And now astronomers have used data from NASA’s Cassini-Huygens mission to map the entire surface of Titan for the first time.  Their work has found a global terrain of mountains, plains, valleys, craters and lakes .  Again, this makes Titan unlike anywhere else in the solar system other than Earth.

“Titan has an atmosphere like Earth. It has wind, it has rain, it has mountains,” said Rosaly Lopes, a planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena.  She and her colleagues wove together images and radar measurements taken by the spacecraft to produce the first global map of the moon.

“Titan has an active methane-based hydrologic cycle that has shaped a complex geologic landscape, making its surface one of most geologically diverse in the solar system,” she said.  “It’s a really very interesting world, and one of the best places in the solar system to look for life,”

Cassini orbited Saturn from 2004 to 2017 and collected vast amounts of information about the ringed gas giant and its moons. The mission included more than 100 fly-bys of Titan,  which allowed researchers to study the moon’s surface through its thick atmosphere and survey its terrain in unprecedented detail.

The first global geologic map of Titan is based on radar and visible-light images from NASA’s Cassini mission.

Their work, which now adds the surface of Titan to the kind of geological mapping done of the surfaces of Mars, Mercury and our moon, was published in Nature Astronomy.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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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

Exoplanets Discoveries Flood in From TESS

NASA’s Transiting Exoplanet Survey Satellite (TESS) has hundreds of “objects of interest” waiting to be confirmed as planets in the data from the space telescope’s four cameras.  These three were the first confirmed TESS discoveries, identified last year during its first three months of observing. By the time the mission is done, TESS’s wide-field cameras will have covered the whole sky in search of transiting exoplanets around 200,000 of the nearest (and brightest) stars. (NASA / MIT / TESS)

The newest space telescope in the sky — NASA’s Transiting Exoplanet Survey Satellite, TESS — has been searching for exoplanets for less than a year, but already it has quite a collection to its name.

The TESS mission is to find relatively nearby planets orbiting bright and stable suns, and so expectations were high from the onset about the discovery of important new planets and solar systems.  At a meeting this week at the Massachusetts Institute of Technology devoted to TESS  results,  principal investigator George Ricker pronounced the early verdict.

The space telescope, he said,  “has far exceeded our most optimistic hopes.”  The count is up to 21 new planets and 850 additional  candidate worlds waiting to be confirmed.

Equally or perhaps more important is that the planets and solar systems being discovered promise important results.  They have not yet included any Earth-sized rocky planet in a sun’s habitable zone — what is generally considered the most likely, though hardly the only, kind of planet to harbor life — but they did include planets that offer a great deal when it comes to atmospheres and how they can be investigated.

This infographic illustrates key features of the TOI 270 system, located about 73 light-years away in the southern constellation Pictor. The three known planets were discovered by NASA’s Transiting Exoplanet Survey Satellite through periodic dips in starlight caused by each orbiting world. Insets show information about the planets, including their relative sizes, and how they compare to Earth. Temperatures given for TOI 270’s planets are equilibrium temperatures, (NASA’s Goddard Space Flight Center/Scott Wiessinger)

One of the newest three-planet system is called TOI-270, and it’s about 75 light years from Earth. The star at the center of the system is a red dwarf, a bit less than half the size of the sun.

Despite its small size, it’s brighter than most of the nearby stars we know host planets. And it’s stable, making its solar system especially valuable.

Read more

Curiosity Rover as Seen From High Above by Mars Orbiter

A camera on board NASA’s Mars Reconnaissance Orbiter recently spotted the Curiosity rover in Gale Crater.  The image is color-enhanced to allow surface features to become more visible. (NASA/JPL-Caltech)

This is Apollo memory month, when the 50th anniversary arrives of the first landing of astronauts on the moon.  It was a very big deal and certainly deserves attention and applause.

But there’s something unsettling about the anniversary as well, a sense that the human exploration side of NASA’s mission has disappointed and that its best days were many decades ago.   After all, it has been quite a few years now since NASA has been able to even get an astronaut to the International Space Station without riding in a Russian capsule.

There have been wondrous (and brave) NASA human missions since Apollo — the several trips to the Hubble Space Telescope for emergency repair and upgrade come to mind — but many people who equate NASA with human space exploration are understandably dismayed.

This Many Worlds column does not focus on human space exploration, but rather on the science coming from space telescopes, solar system missions, and the search for life beyond Earth.

And as I have argued before, the period that following the last Apollo mission and began with the 1976 Viking landings on Mars has been — and continues to be — the golden era of space science.

This image of Curiosity,  which is now exploring an area that has been named Woodland Bay in Gale Crater, helps make the case.

Taken on May 31 by the HiRISE camera of NASA’s Mars Reconnaissance Orbiter (MRO), it shows the rover in a geological formation that holds remains of ancient clay.  This is important because clay can be hospitable to life, and Curiosity has already proven that Mars once had the water, organic compounds and early climate to support life.

The MRO orbits between 150 and 200 miles above Mars, so this detailed image is quite a feat.

The arm of the Curiosity rover examines the once-watery remains at Woodland Bay, Gale Crater. (NASA/JPL-Caltech)

Curiosity landed on Mars for what was planned as a mission of two years-plus. That was seven years ago this coming August.

The rover has had some ups and downs and has moved more slowly than planned, but it remains in motion — collecting paradigm-shifting information, drilling into the Mars surface, taking glorious images and making its way up the slopes of Gale Crater. … Read more

NASA Announces Astrobiology Mission to Titan

 

The Dragonfly drone has been selected as the next New Frontiers mission, this time to Saturn’s moon Titan.  Animation of the vehicle taking off from the surface of the moon. (NASA)

A vehicle that flies like a drone and will try to unravel some of the mysteries of Saturn’s moon Titan was selected yesterday to be the next New Frontiers mission to explore the solar system.

Searching for the building blocks of life,  the Dragonfly mission will be able to fly multiple sorties to sample and examine sites around Saturn’s icy moon.

Titan has a thick atmosphere and features a variety of hydrocarbons, with rivers and lakes of methane, ethane and natural gas, as well as and precipitation cycles like on Earth.  As a result, Dragonfly has been described as an astrobiology mission because it will search for signs of the prebiotic environments like those on Earth that gave rise to life.

“Titan is unlike any other place in the solar system, and Dragonfly is like no other mission,” said Thomas Zurbuchen, NASA’s associate administrator for science at the agency headquarters in Washington.

“It’s remarkable to think of this rotorcraft flying miles and miles across the organic sand dunes of Saturn’s largest moon, exploring the processes that shape this extraordinary environment. Dragonfly will visit a world filled with a wide variety of organic compounds, which are the building blocks of life and could teach us about the origin of life itself.”

 

Saturn’s moon Titan is significantly larger than our moon, and larger than the planet Mercury. It features river channels of ethane and methane, and lakes of liquified natural gas. It is the only other celestial body in our solar system that has flowing liquid on its surface. (NASA)

As described in a NASA release, Titan is an analog to the very early Earth, and can provide clues to how life may have arisen on our planet.

Dragonfly will explore environments ranging from organic dunes to the floor of an impact crater where liquid water and complex organic materials key to life once existed together for possibly tens of thousands of years. Its instruments will study how far prebiotic chemistry may have progressed.

They also will investigate the moon’s atmospheric and surface properties and its subsurface ocean and liquid reservoirs. Additionally, instruments will search for chemical evidence of past or extant life.

Because it is so far from the sun, Titan’s surface temperature is around -290 degrees Fahrenheit and its surface pressure is 50 percent higher than Earth’s.… Read more

The Interiors of Exoplanets May Well Hold the Key to Their Habitability

Scientists have had a working — and evolving — understanding of the interior of the Earth for only a century or so.  But determining whether a distant planet is truly habitable may require an understanding of its inner dynamics — which will for sure be a challenge to achieve. (Harvard-Smithsonian Center for Astrophysics)

The quest to find habitable — and perhaps inhabited — planets and moons beyond Earth focuses largely on their location in a solar system and the nature of its host star,  the eccentricity of its orbit, its size and rockiness, and the chemical composition of its atmosphere, assuming that it has one.

Astronomy, astrophysics, cosmochemistry and many other disciplines have made significant progress in characterizing at least some of the billions of exoplanets out there, although measuring the chemical makeup of atmospheres remains a immature field.

But what if these basic characteristics aren’t sufficient to answer necessary questions about whether a planet is habitable?  What if more information — and even more difficult to collect information — is needed?

That’s the position of many planetary scientists who argue that the dynamics of a planet’s interior are essential to understand its habitability.

With our existing capabilities, observing an exoplanet’s atmospheric composition will clearly be the first way to search for signatures of life elsewhere.   But four scientists at the Carnegie Institution of Science — Anat Shahar, Peter Driscoll, Alycia Weinberger, and George Cody — argued in a recent perspective article in Science that a true picture of planetary habitability must consider how a planet’s atmosphere is linked to and shaped by what’s happening in its interior.

They argue that on Earth, for instance, plate tectonics are crucial for maintaining a surface climate where life can fill every niche. And without the cycling of material between the planet’s surface and interior, the convection that drives the Earth’s magnetic field would not be possible and without a magnetic field, we would be bombarded by cosmic radiation.

What makes a planet potentially habitable and what are signs that it is not. This graphic from the Carnegie paper illustrates the differences (Shahar et al.)

 

“The perspective was our way to remind people that the only exoplanet observable right now is the atmosphere, but that the atmospheric composition is very much linked to planetary interiors and their evolution,” said lead author Shahar, who is trained in geological sciences. “If there is a hope to one day look for a biosignature, it is crucial we understand all the ways that interiors can influence the atmospheric composition so that the observations can then be better understood.”

“We need a better understanding of how a planet’s composition and interior influence its habitability, starting with Earth,” she said. 

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Exoplanets With Complex Life May Be Very Rare, Even in Their “Habitable Zones”

The term “habitable zone” can be a misleading one, since it describes a limited number of conditions on a planet to make it hospitable to life. (NASA)

 

For years now, finding planets in the habitable zones of their host stars has been a global astrophysical quest and something of a holy grail.  That distance from a star where temperatures could allow H20 to remain liquid some of the time has been deemed the “Goldilocks” zone where life could potentially emerge and survive.

The term is valuable for sure, but many in the field worry that it can be as misleading or confusing as it is helpful.

Because while the habitable zone is a function of the physics and architecture of a solar system, so much more is needed to make a planet actually potentially habitable.  Does it have an atmosphere?  Does it have a magnetic field. Does it orbit on an elliptical path that takes it too far (and too close) to the sun?  Was it sterilized during the birth of the host star and orbiting planets?  What kind of star does it orbit, and how old and luminous is that star?

And then there’s the sometimes confused understanding that many habitable zones may well support complex, even technologically-advanced life.  They are, after all, habitable.

But as a new paper in the Astrophysical Journal makes clear, the likelihood of a habitable zone planet being able to support complex life — anything beyond a microbe — is significantly limited by the amount of toxic chemicals such as carbon monoxide and excesses of carbon dioxide.

Eddie Schwieterman, a NASA postdoc at the University of California, Riverside and lead author of the article, told me that the odds for complex life on most exoplanets in their habitable zones weren’t great.

“A rough estimate is between 10-20% of habitable zone planets are truly suitable for analogs to humans and animals.” he said. “Of course, being located in this part of the habitable zone isn’t enough by itself – you still need the build-up of oxygen via the evolution of oxygenic photosynthesis and certain planetary biogeochemical cycles.”

 

A rendering of the exoplanet Kepler 442 b, compared in size to  Earth.  Kepler 442 b was detected using the Kepler Space Telescope and is 0ne of a handful of planets found so far deemed to be most likely to be habitable. But it’s 1200 light-years away, so learning its secrets will be challenging.

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