Elizabeth Tasker

Author: Elizabeth Tasker (page 2 of 3)

The Gale Winds of Venus Suggest How Locked Exoplanets Could Escape a Fate of Extreme Heat and Brutal Cold

Two images of the nightside of Venus captured by the IR2 camera on the Akatsuki orbiter in September 2016 (JAXA).

More than two decades before the first exoplanet was discovered, an experiment was performed using a moving flame and liquid mercury that could hold the key to habitability on tidally locked worlds.

The paper was published in a 1969 edition of the international journal, Science, by researchers Schubert and Whitehead. The pair reported that when a Bunsen flame was rotated beneath a cylindrical container of mercury, the liquid began to flow around the container in the opposite direction at speeds up to four times greater than the rotation of the flame. The scientists speculated that such a phenomenon might explain the rapid winds on Venus.

On the Earth, the warm equator and cool poles set up a pressure difference that creates our global winds. These winds are deflected westward by the rotation of the planet (the so-called Coriolis force) promoting a zonal (east-west) air flow around the globe. But what would happen if our planet’s rotation slowed? Would our winds just cycle north and south between the equator and poles?

The Moon is tidally locked to the Earth, so only one hemisphere is visible from our planet (Smurrayinchester / wikipedia commons).

Such a slow-rotating scenario may be the lot of almost all rocky exoplanets discovered to date. Planets such as the TRAPPIST-1 system and Proxima Centauri-b all orbit much closer to their star than Mercury, making their faint presence easier to detect but likely resulting in tidal lock. Like the moon orbiting the Earth, planets in tidal lock have one side permanently facing the star, creating a day that is equal to the planet’s year.

The dim stars orbited by these planets can mean they receive a similar level of radiation as the Earth, placing them within the so-called “habitable zone.” However, tidal lock comes with the risk of horrific atmospheric collapse. On the planet side perpetually facing away from the star, temperatures can drop low enough to freeze an Earth-like atmosphere. The air from the dayside would then rush around the planet to fill the void, freezing in turn and causing the planet to lose its atmosphere even within the habitable zone.

The only way this could be prevented is if winds circulating around the planet could redistribute the heat sufficiently to prevent freeze-out. But without a strong Coriolis force from the planet’s rotation, can such winds exist?… Read more

Does Proxima Centauri Create an Environment Too Horrifying for Life?

November 29, 2018 / Elizabeth Tasker / 0 Comments

Artist’s impression of the exoplanet Proxima Centauri b. (ESO/M. Kornmesser)

In 2016, the La Silla Observatory in Chile spotted evidence of possibly the most eagerly anticipated exoplanet in the Galaxy. It was a world orbiting the nearest star to the sun, Proxima Centauri, making this our closest possible exoplanet neighbour. Moreover, the planet might even be rocky and temperate.

Proxima Centauri b had been discovered by discerning a periodic wobble in the motion of the star. This revealed a planet with a minimum mass 30% larger than the Earth and an orbital period of 11.2 days. Around our sun, this would be a baking hot world.

But Proxima Centauri is a dim red dwarf star and bathes its closely orbiting planet in a level of radiation similar to that received by the Earth. If the true mass of the planet was close to the measured minimum mass, this meant Proxima Centauri b would likely be a rocky world orbiting within the habitable zone.

Comparison of the orbit of Proxima Centauri b with the same region of the solar system. Proxima Centauri is smaller and cooler than the sun and the planet orbits much closer to its star than Mercury. As a result it lies well within the habitable zone. (ESO/M. Kornmesser/G. Coleman.)

Sitting 4.2 light years from our sun, a journey to Proxima Centauri b is still prohibitively long.

But as our nearest neighbor, the exoplanet is a prime target for the upcoming generation of telescopes that will attempt to directly image small worlds. Its existence was also inspiration for privately funded projects to develop faster space travel for interstellar distances.

Yet observations taken around the same time as the La Silla Observatory discovery were painting a very different picture of Proxima Centauri. It was a star with issues.

This set of observations were taken with Evryscope; an array of small telescopes that was watching stars in the southern hemisphere. What Evryscope spotted was a flare from Proxima Centauri that was so bright that the dim red dwarf star became briefly visible to the naked eye.

Flares are the sudden brightening in the atmosphere of a star that release a strong burst of energy. They are often accompanied by a large expulsion of plasma from the star known as a “coronal mass ejection”. Flares from the sun are typically between 10²⁷ – 10³² erg of energy, released in a few tens of minutes.… Read more

What Would Happen If Mars And Venus Swapped Places?

October 24, 2018 / Elizabeth Tasker / 0 Comments

Venus, Earth and Mars (ESA).

What would happen if you switched the orbits of Mars and Venus? Would our solar system have more habitable worlds?

It was a question raised at the “Comparative Climatology of Terrestrial Planets III”; a meeting held in Houston at the end of August. It brought together scientists from disciplines that included astronomers, climate science, geophysics and biology to build a picture of what affects the environment on rocky worlds in our solar system and far beyond.

The question regarding Venus and Mars was proposed as a gedankenexperiment or “thought experiment”; a favorite of Albert Einstein to conceptually understand a topic. Dropping such a problem before the interdisciplinary group in Houston was meat before lions: the elements of this question were about to be ripped apart.

The Earth’s orbit is sandwiched between that of Venus and Mars, with Venus orbiting closer to the sun and Mars orbiting further out. While both our neighbors are rocky worlds, neither are top picks for holiday destinations.

Mars has a mass of just one-tenth that of Earth, with a thin atmosphere that is being stripped by the solar wind; a stream of high energy particles that flows from the sun. Without a significant blanket of gases to trap heat, temperatures on the Martian surface average at -80°F (-60°C). Notably, Mars orbits within the boundaries of the classical habitable zone (where an Earth-like planet could maintain surface water) but the tiny planet is not able to regulate its temperature as well as the Earth might in the same location.

The classical habitable zone around our sun marks where an Earth-like planet could support liquid water on the surface (Cornell University).

Unlike Mars, Venus has nearly the same mass as the Earth. However, the planet is suffocated by a thick atmosphere consisting principally of carbon dioxide. The heat-trapping abilities of these gases soar surface temperatures to above a lead-melting 860°F (460°C).

But what if we could switch the orbits of these planets to put Mars on a warmer path and Venus on a cooler one? Would we find that we were no longer the only habitable world in the solar system?

“Modern Mars at Venus’s orbit would be fairly toasty by Earth standards,” suggests Chris Colose, a climate scientist based at the NASA Goddard Institute for Space Studies and who proposed the topic for discussion.

Dragging the current Mars into Venus’s orbit would increase the amount of sunlight hitting the red planet.… Read more

Prepare For Lift-off! BepiColombo Launches For Mercury

October 18, 2018 / Elizabeth Tasker / 0 Comments

Artist illustration of the BepiColombo orbiters, MIO and Bepi, around Mercury (JAXA).

This Friday (October 19) at 10:45pm local time in French Guinea, a spacecraft is set to launch for Mercury. This is the BepiColombo mission which will begin its seven year journey to our solar system’s innermost planet. Surprisingly, the science goals for investigating this boiling hot world are intimately linked to habitability.

Mercury orbits the sun at an average distance of 35 million miles (57 million km); just 39% of the distance between the sun and the Earth. The planet therefore completes a year in just 88 Earth days.

The close proximity to the sun puts Mercury in a 3:2 tidal lock, meaning the planet rotates three times for every two orbits around the sun. (By contrast, our moon is in a 1:1 tidal lock and rotates once for every orbit around the Earth.) With only a tenuous atmosphere to redistribute heat, this orbit results in extreme temperatures between about -290°F and 800°F (-180°C to 427°C). The overall picture is one of the most inhospitable of worlds, so what do we hope to learn from this barren and baked land?

BepiColombo is a joint mission between the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA). It consists of two orbiters, one built by each space agency. The mission is named after Giuseppe “Bepi” Colombo, an Italian mathematician who calculated the orbit of the first mission to Mercury —NASA’s Mariner 10— such that it could make repeated fly-bys of the planet.

When Mariner 10 reached Mercury in the mid-1970s, it made an astonishing discovery: the planet had a weak magnetic field. The Earth also has a magnetic field that is driven by movement in its molten iron core.

However, with a mass of only 5.5% that of the Earth, the interior of Mercury was expected to have cooled sufficiently since its formation for the core to have solidified and jammed the breaks on magnetic field generation. This is thought to have happened to Mars, which is significantly larger than Mercury with a mass around 10% that of the Earth. So how does Mercury hold onto its field?

The discoveries only got stranger with the arrival of NASA’s MESSENGER mission in 2011. MESSENGER discovery that Mercury’s magnetic field was off-set, with the center shifted northwards by a distance equal to 20% of the planet’s radius.

The mysteries also do not end with Mercury’s wonky magnetic field.… Read more

Asteroid Remains Around Dead Stars Reveal the Likely Fate of Our Solar System

June 28, 2018 / Elizabeth Tasker / 0 Comments

Artist concept of an asteroid breaking up. (NASA/JPL-Caltech)

June 30th has been designated “Asteroid Day” to promote awareness of these small members of our solar system. But while asteroids are often discussed in the context of the risk they might pose to the Earth, their chewed up remains around other stars may also reveal the fate of our solar system.

It is 6.5 billion years into our future. The sun has fused hydrogen into a core of heavier helium. Compressed by its own gravity, the helium core releases heat and the sun begins to swell. It is the end of our star’s life, but what will happen to the solar system?

While very massive stars end their element-fusing days in a colossal explosion known as a supernovae, the majority of stars in our galaxy will take a less dramatic exit.

Our sun’s helium core will fuse to form carbon but there is not enough mass to achieve the crushing compression needed for the creation of heavier elements. Instead, the outer layers of the dying star will be blown away to leave a dense remnant with half the mass of our current sun, but squeezed down to the size of the Earth. This is a white dwarf; the most common of all stellar ends.

The life cycle of our sun

The white dwarf rapidly cools to become a dim twinkle in the sky. Within a few million years, our white dwarf will be less luminous that the sun today. Within 100 million years, it will be dimmer by a factor of 100. But examination of white dwarfs in our galaxy reveals this gentle dimming of the lights is not as peaceful as first appears.

The remnants of stars too light to fuse carbon, white dwarfs have atmospheres that should be thin shells of residue hydrogen and helium. Instead, observations have detected 20 different heavy elements in this envelope of gases that include rock-forming elements such as silicon and iron and volatiles such as carbon and nitrogen.

Infrared observations of over forty white dwarfs have additionally revealed compact dusty discs circling the dead stars. Sitting within the radius of a regular star, these could not have formed before the star shrank into a white dwarf. These must be the remains of what occurred as the star morphed from a regular fusion burner into a white dwarf.

This grizzly tale begins with the star’s expansion.… Read more

Know Thy Star, Know Thy Planet: How Gaia is Helping Nail Down Planet Sizes

May 18, 2018 / Elizabeth Tasker / 0 Comments

Gaia’s all-sky view of our Milky Way and neighboring galaxies. (ESA/Gaia/DPAC)

Last month, the European Space Agency’s Gaia missio n released the most accurate catalogue to date of positions and motions for a staggering 1.3 billion stars.

Let’s do a few comparisons so we can be suitably amazed. The total number of stars you can see without a telescope is less than 10,000. This includes visible stars in both the northern and southern hemispheres, so looking up on a very dark night will allow you to count only about half this number.

The data just released from Gaia is accurate to 0.04 milli-arcseconds. This is a measurement of the angle on the sky, and corresponds to the width of a human hair at a distance of over 300 miles (500 km.) These results are from 22 months of observations and Gaia will ultimately whittle down the stellar positions to within 0.025 milli-arcseconds, the width of a human hair at nearly 680 miles (1000 km.)

OK, so we are now impressed. But why is knowing the precise location of stars exciting to planet hunters?

The reason is that when we claim to measure the radius or mass of a planet, we are almost always measuring the relative size compared to the star. This is true for all planets discovered via the radial velocity and transit techniques — the most common exoplanet detection methods that account for over 95% of planet discoveries.

It means that if we underestimate the star size, our true planet size may balloon from being a close match to the Earth to a giant the size of Jupiter. If this is true for many observed planets, then all our formation and evolution theories will be a mess.

The size of a star is estimated from its brightness. Brightness depends on distance, as a small, close star can appear as bright as a distant giant. Errors in the precise location of stars therefore make a big mess of exoplanet data.

An artist’s impression of the Gaia spacecraft — which is on a mission to chart a three-dimensional map of our Milky Way. In the process it will expand our understanding of the composition, formation and evolution of the galaxy. (ESA/D. Ducros)

This issue has been playing on the minds of exoplanet hunters.

In 2014, a journal paper authored by Fabienne Bastien from Vanderbilt University suggested that nearly half of the brightest stars observed by the Kepler Space Telescope are not regular stars like our sun, but actually are distant and much larger sub-giant stars.… Read more

NASA’s Planet-Hunter TESS Has Just Been Launched to Check Out the Near Exoplanet Neighborhood

April 18, 2018 / Elizabeth Tasker / 0 Comments

A SpaceX Falcon 9 rocket transporting the TESS satellite lifts off from launch complex 40 at the Cape Canaveral Air Force Station in Cape Canaveral, Fla., Wednesday, April 18, 2018. The space telescope will survey almost the entire sky, staring at the brightest, closest stars in an effort to find any planets that might be encircling them. (AP Photo/John Raoux)

On January 5, 2010, NASA issued landmark press release : the Kepler Space Telescope had discovered its first five new extra-solar planets.

The previous twenty years had seen the discovery of just over 400 planets beyond the solar system. The majority of these new worlds were Jupiter-mass gas giants, many bunched up against their star on orbits far shorter than that of Mercury. We had learnt that our planetary system was not alone in the Galaxy, but small rocky worlds on temperate orbits might still have been rare.

Based on just six weeks of data, these first discoveries from Kepler were also hot Jupiters; the easiest planets to find due to their large size and swiftly repeating signature as they zipped around the star. But expectations were high that this would be just the beginning.

“We expected Jupiter-size planets in short orbits to be the first planets Kepler could detect,” said Jon Morse, director of the Astrophysics Division at NASA Headquarters at the time the discovery was announced. “It’s only a matter of time before more Kepler observations lead to smaller planets with longer period orbits, coming closer and closer to the discovery of the first Earth analog.”

Morse’s prediction was to prove absolutely right. Now at the end of its life, the Kepler Space Telescope has found 2,343 confirmed planets, 30 of which are smaller than twice the size of the Earth and in the so-called “Habitable Zone”, meaning they receive similar levels of insolation –the amount of solar radiation reaching a given area–to our own planet.

Yet, the question remains: were any of these indeed Earth analogs?

In just a few decades, thanks to Kepler, the Hubble Space Telescope and scores of astronomers at ground-based observatories, we have gone from suspecting the presence of exoplanets to knowing there are more exoplanets than stars in our galaxy. (NASA/Ames Research Station; Jessie Dotson and Wendy Stenzel)

It was a question that Kepler was not equipped to answer. Kepler identifies the presence of a planet by looking for the periodic dip in starlight as a planet passes across the star’s surface.… Read more

The Just-Approved European ARIEL Mission Will Be First Dedicated to Probing Exoplanet Atmospheres

March 29, 2018 / Elizabeth Tasker / 0 Comments

The Ariel space telescope will explore the atmospheres of exoplanets. (Artist impression, ESA)

The European Space Agency (ESA) has approved the ARIEL space mission—the world’s first dedicated exoplanet atmosphere sniffer— to fly in 2028.

ARIEL stands for the “Atmospheric Remote-sensing Infrared Exoplanet Large-Survey mission.” It is a space telescope that can detect which atoms and molecules are present in the atmosphere of an exoplanet.

The mission was selected as a medium class mission in the ESA Cosmic Vision program; the agency’s decadal plan for space missions that spans 2015 – 2025.

One of the central themes for Cosmic Vision is uncovering the conditions for planet formation and the origins of life. This has resulted in three dedicated exoplanet missions within the same decadal plan. ARIEL will join CHEOPS (in the small class mission category) and PLATO (another medium class mission) in studying worlds beyond our own sun.

Yet ARIEL is a different type of telescope from the other exoplanet-focused missions. To understand why, we need to examine what properties we can observe of these distance exo-worlds.

Exoplanet missions can be broadly divided into two types. The first type are the exoplanet hunter missions that search the skies for new worlds.

These are spacecraft and instruments such as the NASA Kepler Space Telescope. Since it launched in 2009, Kepler has been an incredibly prolific planet hunter. The telescope has found thousands of planets, modeled their orbits and told us about the distribution of their sizes.

From Kepler, we have learnt that planet formation is common, that it can occur around stars far different from our own sun, and that these worlds can have a vast range of sizes and myriad of orbits quite unlike our own Solar System.

Current and future (or proposed) space missions with capacities to identify and characterize exoplanets. The very productive CoRotT mission is, however, missing. It searched for and found many exoplanets from 2006 to 2013. (NASA,ESA: T. Wynne/JPL, composited by Barbara Aulicino)

However, the information Kepler is able to provide about individual planets is very limited. The telescope monitors stars for the tiny drop in light as the planet crosses (or “transits”) the star’s surface. From this, astronomers can measure the radius of the planet and its orbital period but nothing about the planet’s surface conditions.

The result is a little like knowing the number of students and distribution of grades in a particular school, but having no idea if the student who sits in the third row actually likes math.… Read more

To Understand Habitability, We Need to Return to Venus

February 8, 2018 / Elizabeth Tasker / 1 Comment

This image shows the night side of Venus in thermal infrared. It is a false-color image using data from the Japanese spacecraft Akatsuki’s IR2 camera in two wavelengths, 1.74 and 2.26 microns. Darker regions denote thicker clouds, but changes in color can also denote differences in cloud particle size or composition from place to place. JAXA / ISAS / DARTS / Damia Bouic

“You can feel what it’s like on Venus here on Earth,” said Kevin McGouldrick from the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder. “Heat a hot plate until it glows red, place your palm on its surface and then run over that hand with a truck.”

The surface of Venus is a hellish place. Suffocated by a thick atmosphere, pressure on the Venusian surface is 92 times greater than on the surface of Earth. Temperatures sit at a staggering 863°F (462°C), which is sufficient to melt lead.

The longest a spacecraft has survived in these conditions is a mere 127 minutes; a record set by the Russian Venera 13 mission over 35 years ago.

As the brightest planet in the night sky, Venus allured ancient astronomers into naming the world after the Roman mythological goddess of love and beauty. This now seems an ironic choice, but the contrast between distant observation and surface conditions produces an apt juxtaposition for exoplanets.

The comparison has led to an article in Nature Geoscience by McGouldrick and a nine author white paper advising on astrobiology strategy for the National Science Foundation. The conclusion of both publications echoes the irony of Venus’s name: we need to return to the inferno of Venus to understand habitable worlds.

A portion of western Eistla Regio is displayed in this three-dimensional perspective view of the surface of Venus. Synthetic aperture radar data from the spacecraft Magellan is combined with radar altimetry to develop a three-dimensional map of the surface. Rays cast in a computer intersect the surface to create a three-dimensional perspective view. The simulated hues are based on color images recorded by the Soviet Venera 13 and 14 spacecraft. The image, a frame from a video released in 1991, was produced at NASA’s JPL Multimission Image Processing Laboratory.

In the last 25 years, scientists have discovered over 3,500 extrasolar planets. The vast majority of these worlds have not been imaged directly, but are detected by tiny influences on their host star.… Read more

Artificial Intelligence Has Just Found Two Exoplanets: What Does This Mean For Planet Hunting?

December 18, 2017 / Elizabeth Tasker / 0 Comments

There are now two known eight-planet solar systems in the galaxy. Artificial intelligence was used to comb through the data collected three years ago by the Kepler Space Telescope and its algorithms helped find Kepler 90-1, the eight planet in that solar system. (NASA)

The media was abuzz last week with the latest NASA news conference. A neural network — a form of artificial intelligence or machine learning — developed at Google had found two planets in data previously collected by NASA’s prolific Kepler Space Telescope. It’s a technique that could ultimately track-down our most Earth-like planets.

The new exoplanets orbit stars already known to host planetary systems, Kepler-90 and Kepler-80. While both are only slightly larger than the Earth, their two-week orbits makes these worlds too hot to be considered likely candidates for hosting life. Moreover, the systems are thousands of light years away, putting the planets out of range of atmospheric studies that could test their habitability.

With over 3,500 exoplanets already discovered, you might be forgiven for finding these additions underwhelming. However, while other planets in the same system have been known about for several years, these two Earth-sized worlds were previously overlooked. The difference is not a new telescope, but an exploration of the data with a different kind of brain.

The Kepler Space Telescope searches for planets using the transit technique; detecting small dips in amount of starlight as the planet passes in front of the star. As planets are much smaller than stars, picking out this tiny light drop is a tricky task. For a Jupiter-sized planet orbiting a star like our Sun, the decrease in brightness is only about 1%. For an Earth-sized planet, the signal becomes so small it is right on the edge of what Kepler is able to detect. This makes their dim wink extremely difficult to spot in the data.

Kepler Space Telescope collected data on planet transits around distant stars for four years, and the information has provided — and will continue providing — a goldmine for planet hunters. A severe malfunction in 2013 had robbed Kepler of its ability to stay pointed at a target without drifting off course, but the spacecraft was stabilized and readjusted to observe a different set of stars. (NASA)

The discovery paper published in the Astronomical Journal combined the expertise of Christopher Shallue from Google’s artificial intelligence project, Google Brain, and Andrew Vanderburg, a NASA Sagan Postdoctoral Fellow and astronomer at the University of Texas at Austin.… Read more

Many Worlds