NASA’s Next Exoplanet Hunter Moves Into Development

A conceptual image of the Transiting Exoplanet Survey Satellite. Image Credit: MIT

NASA’s ongoing hunt for exoplanets has entered a new phase as NASA officially confirmed that the Transiting Exoplanet Survey Satellite (TESS) is moving into the development phase. This marks a significant step for the TESS mission, which will search the entire sky for planets outside our solar system (a.k.a. exoplanets). Designed as the first all-sky survey, TESS will spend two years of an overall three-year mission searching both hemispheres of the sky for nearby exoplanets.

Previous sky surveys with ground-based telescopes have mainly picked out giant exoplanets. In contrast, TESS will examine a large number of small planets around the very brightest stars in the sky. TESS will then record the nearest and brightest main sequence stars hosting transiting exoplanets, which will forever be the most favorable targets for detailed investigations. During the third year of the TESS mission, ground-based astronomical observatories will continue monitoring exoplanets identified by the TESS spacecraft.

“This is an incredibly exciting time for the search of planets outside our solar system,” said Mark Sistilli, the TESS program executive from NASA Headquarters, Washington. “We got the green light to start building what is going to be a spacecraft that could change what we think we know about exoplanets.”

“During its first two years in orbit, the TESS spacecraft will concentrate its gaze on several hundred thousand specially chosen stars, looking for small dips in their light caused by orbiting planets passing between their host star and us,” said TESS Principal Investigator George Ricker of the Massachusetts Institute of Technology..

Artistic representations of the only known planets around other stars (exoplanets) with any possibility to support life as we know it. Credit: Planetary Habitability Laboratory, University of Puerto Rico, Arecibo.
Artistic representations of known exoplanets with any possibility to support life. Image Credit: Planetary Habitability Laboratory, University of Puerto Rico, Arecibo.

All in all, TESS is expected to find more than 5,000 exoplanet candidates, including 50 Earth-sized planets. It will also find a wide array of exoplanet types, ranging from small, rocky planets to gas giants. Some of these planets could be the right sizes, and orbit at the correct distances from their stars, to potentially support life.

“The most exciting part of the search for planets outside our solar system is the identification of ‘earthlike’ planets with rocky surfaces and liquid water as well as temperatures and atmospheric constituents that appear hospitable to life,” said TESS Project Manager Jeff Volosin at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Although these planets are small and harder to detect from so far away, this is exactly the type of world that the TESS mission will focus on identifying.”

Now that NASA has confirmed the development of TESS, the next step is the Critical Design Review, which is scheduled to take place in 2015. This would clear the mission to build the necessary flight hardware for its proposed launch in 2017.

“After spending the past year building the team and honing the design, it is incredibly exciting to be approved to move forward toward implementing NASA’s newest exoplanet hunting mission,” Volosin said.

TESS is designed to complement several other critical missions in the search for life on other planets. Once TESS finds nearby exoplanets to study and determines their sizes, ground-based observatories and other NASA missions, like the James Webb Space Telescope, would make follow-up observations on the most promising candidates to determine their density and other key properties.

The James Webb Space Telescope. Image Credit: NASA/JPL
The James Webb Space Telescope. Image Credit: NASA/JPL

By figuring out a planet’s characteristics, like its atmospheric conditions, scientists could determine whether the targeted planet has a habitable environment.

“TESS should discover thousands of new exoplanets within two hundred light years of Earth,” Ricker said. “Most of these will be orbiting bright stars, making them ideal targets for characterization observations with NASA’s James Webb Space Telescope.”

“The Webb telescope and other teams will focus on understanding the atmospheres and surfaces of these distant worlds, and someday, hopefully identify the first signs of life outside of our solar system,” Volosin said.

TESS will use four cameras to study sections of the sky’s north and south hemispheres, looking for exoplanets. The cameras would cover about 90 percent of the sky by the end of the mission.

This makes TESS an ideal follow-up to the Kepler mission, which searches for exoplanets in a fixed area of the sky. Because the TESS mission surveys the entire sky, TESS is expected to find exoplanets much closer to Earth, making them easier for further study.

In addition, Ricker said TESS would provide precision, full-frame images for more than 20 million bright stars and galaxies.

“This unique new data will comprise a treasure trove for astronomers throughout the world for many decades to come,” Ricker said.

Now that TESS is cleared to move into the next development stage, it can continue towards its goal of being a key part of NASA’s search for life beyond Earth.

“I’m still hopeful that in my lifetime, we will discover the existence of life outside of our solar system and I’m excited to be part of a NASA mission that serves as a key stepping stone in that search,” Volosin said.

Further Reading: NASA

Two Comet Groups Discovered Around Beta Pictoris

Between the years 2003 and 2011, the High Accuracy Radial velocity Planet Searcher – better known as HARPS – made more than a thousand observations of nearby star, Beta Pictoris. On board the ESO 3.6-metre telescope at the La Silla Observatory in Chile, the sensitive instrument normally combs the sky nightly in search of exoplanets, but lately it has contributed to another astounding discovery… exocomets!

Located about 63 light-years from the Sun, Beta Pictoris is a youthful star, estimated to be only around 20 million years old. Keeping it company in space is a vast disc of material. This swarm of gas and dust is the beginnings of an active planetary system and was likely created by the destruction of comets and collisions of rocky bodies like asteroids. Now a French team using HARPS has been able to create the most complete catalog of comets to date from this system. Researchers have found no less than five hundred comets belonging to Beta Pictoris and they divide in two unique branches of exocomets. Split into both old and new, these two active flows behave much like our own cometary groups… They have either made many trips around the parent star or are the product of a recent breakup of one or more objects.

Flavien Kiefer (IAP/CNRS/UPMC), lead author of the new study, sets the scene: “Beta Pictoris is a very exciting target! The detailed observations of its exocomets give us clues to help understand what processes occur in this kind of young planetary system.”

Beta Pictoris is located about 60 light-years away towards the constellation of Pictor (the Painter's Easel) and is one of the best-known examples of a star surrounded by a dusty debris disc. Earlier observations showed a warp of the disc, a secondary inclined disc and comets falling onto the star, all indirect, but tell-tale signs that strongly suggested the presence of a massive planet. Observations done with the NACO instrument on ESO’s Very Large Telescope in 2003, 2008 and 2009, have proven the presence of a planet around Beta Pictoris. It is located at a distance between 8 and 15 times the Earth-Sun separation — or Astronomical Units — which is about the distance Saturn is from the Sun. The planet has a mass of about nine Jupiter masses and the right mass and location to explain the observed warp in the inner parts of the disc. This image, based on data from the Digitized Sky Survey 2, shows a region of approximately 1.7 x 2.3 degrees around Beta Pictoris.  Credit: ESO/Sky Survey II
Beta Pictoris is located about 60 light-years away towards the constellation of Pictor (the Painter’s Easel) and is one of the best-known examples of a star surrounded by a dusty debris disc. Earlier observations showed a warp of the disc, a secondary inclined disc, and comets falling onto the star, all indirect, but tell-tale signs that strongly suggested the presence of a massive planet. Observations done with the NACO instrument on ESO’s Very Large Telescope in 2003, 2008, and 2009, have proven the presence of a planet around Beta Pictoris. It is located at a distance between 8 and 15 times the Earth-Sun separation — or Astronomical Units — which is about the distance Saturn is from the Sun. The planet has a mass of about nine Jupiter masses and the right mass and location to explain the observed warp in the inner parts of the disc. This image, based on data from the Digitized Sky Survey 2, shows a region of approximately 1.7 x 2.3 degrees around Beta Pictoris. Credit: ESO/Sky Survey II

Just like discovering planets through the transit method, astronomers believe exocomets can cause a disturbance in the amount of light we can see from a given star. When these icy travelers exhaust themselves, their gas and dust tails could absorb a portion of the star light passing through them. For nearly three decades scientists had been aware of minute changes in the light from Beta Pictoris, but attributing it to comets was next to impossible to prove. Their tiny light was simply overpowered by the light of the star and could not be imaged from Earth.

Enter HARPS…

Using more than a thousand observations taken by this sensitive equipment, astronomers chose a sample of 493 exocomets unrelated to each other, but sharing in the Beta Pictoris system. Of these, some were dutifully followed for hours at several different times. The size and speed of the gas clouds produced were carefully measured. Researchers were even able to document the orbital properties of some of these exocomets – the size and shape of their passage paths in relation to the parent star allowing scientists to infer their distances.

Knowing that comets exist around other stars is very exciting – and knowing that solar systems around other stars work much like our own is downright rewarding. Through this study, we’re able to take a unique look at what might be several hundreds of exocomets connected to a solitary exo-planet system. What the research has revealed is two distinct branches of the comet family tree. One of these is old comets – their orbit dictated by a single, massive planet. The other half of the family fork belongs to comets that might have arisen from the destruction of a larger object.

The older group behaves in a predictable manner. These exocomets have differing orbital patterns, and their gas and dust production is greatly reduced. If they follow the same rules as the ones in our solar system, it’s typical behavior for a comet which has exhausted its volatiles during multiple trips around the parent star and is also being controlled by the system’s massive planet. This is exciting because it confirms the planet’s presence and distance!

“Moreover, the orbits of these comets (eccentricity and orientation) are exactly as predicted for comets trapped in orbital resonance with a massive planet.” says the science team. “The properties of the comets of the first family show that this planet in resonance must be at about 700 million kilometres from the star – close to where the planet Beta Pictoris b was discovered.”

The second group also behaves in a predictable manner. These exocomets have nearly identical orbits and their emissions are active and radical. Observations of this cometary type tell us they more than likely originated from the destruction of a larger body and the rubble is caught in a orbit which allows the fragments to graze Beta Pictoris. According to the research team: “This makes them similar to the comets of the Kreutz family in the Solar System, or the fragments of Comet Shoemaker-Levy 9, which impacted Jupiter in July 1994.”

Flavien Kiefer concludes: “For the first time a statistical study has determined the physics and orbits for a large number of exocomets. This work provides a remarkable look at the mechanisms that were at work in the Solar System just after its formation 4.5 billion years ago.”

Original Story Source: “Two Families of Comets Found Around Nearby Star – Biggest census ever of exocomets around Beta Pictoris” – ESO Science News Release

Planets Plentiful Around Abundant Red Dwarf Stars, Study Says

Good news for planet-hunters: planets around red dwarf stars are more abundant than previously believed, according to new research. A new study — which detected eight new planets around these stars — says that “virtually” all red dwarfs have planets around them. Moreover, super-Earths (planets that are slightly larger than our own) are orbiting in the habitable zone of about 25% of red dwarfs nearby Earth.

“We are clearly probing a highly abundant population of low-mass planets, and can readily expect to find many more in the near future – even around the very closest stars to the Sun,” stated Mikko Tuomi, who is from the University of Hertfordshire’s centre for astrophysics research and lead author of the study.

The find is exciting for astronomers as red dwarf stars make up about 75% of the universe’s stars, the study authors stated.

The researchers looked at data from two planet-hunting surveys: HARPS (High Accuracy Radial Velocity Planet Searcher) and UVES (Ultraviolet and Visual Echelle Spectrograph), which are both at the European Southern Observatory in Chile. The two instruments measure the effect a planet has on its parent star, specifically by examining the gravitational “wobble” the planet’s orbit produces.

An artist's concept of a rocky world orbiting a red dwarf star. (Credit: NASA/D. Aguilar/Harvard-Smithsonian center for Astrophysics).
An artist’s concept of a rocky world orbiting a red dwarf star. (Credit: NASA/D. Aguilar/Harvard-Smithsonian center for Astrophysics).

Putting the information from both sets of data together, this amplified the planet “signals” and revealed eight planets around red dwarf stars, including three super-Earths in habitable zones. The researchers also applied a probability function to estimate how abundant planets are around this type of star.

The planets are between 15 and 80 light years away from Earth, and add to the 17 other planets found around low-mass dwarfs. Scientists also detected 10 weaker signals that could use more investigation, they said.

The study will be available shortly in the Monthly Notices of the Royal Astronomical Society and is available in preprint version at this link.

Source: University of Hertfordshire

New Technique Finds Water in Exoplanet Atmospheres

As more and more exoplanets are identified and confirmed by various observational methods, the still-elusive “holy grail” is the discovery of a truly Earthlike world… one of the hallmarks of which is the presence of liquid water. And while it’s true that water has been identified in the thick atmospheres of “hot Jupiter” exoplanets before, a new technique has now been used to spot its spectral signature in yet another giant world outside our solar system — potentially paving the way for even more such discoveries.

Researchers from Caltech, Penn State University, the Naval Research Laboratory, the University of Arizona, and the Harvard-Smithsonian Center for Astrophysics have teamed up in an NSF-funded project to develop a new way to identify the presence of water in exoplanet atmospheres.

Previous methods relied on specific instances such as when the exoplanets — at this point all “hot Jupiters,” gaseous planets that orbit closely to their host stars — were in the process of transiting their stars as viewed from Earth.

This, unfortunately, is not the case for many extrasolar planets… especially ones that were not (or will not be) discovered by the transiting method used by observatories like Kepler.

Watch: Kepler’s Universe: More Planets in Our Galaxy Than Stars

So the researchers turned to another method of detecting exoplanets: radial velocity, or RV. This technique uses visible light to watch the motion of a star for the ever-so-slight wobble created by the gravitational “tug” of an orbiting planet. Doppler shifts in the star’s light indicate motion one way or another, similar to how the Doppler effect raises and lowers the pitch of a car’s horn as it passes by.

The two Keck 10-meter domes atop Mauna Kea. (Rick Peterson/WMKO)
The two Keck 10-meter domes atop Mauna Kea. (Rick Peterson/WMKO)

But instead of using visible wavelengths, the team dove into the infrared spectrum and, using the Near Infrared Echelle Spectrograph (NIRSPEC) at the W. M. Keck Observatory in Hawaii, determined the orbit of the relatively nearby hot Jupiter tau Boötis b… and in the process used its spectroscopy to identify water molecules in its sky.

“The information we get from the spectrograph is like listening to an orchestra performance; you hear all of the music together, but if you listen carefully, you can pick out a trumpet or a violin or a cello, and you know that those instruments are present,” said Alexandra Lockwood, graduate student at Caltech and first author of the study. “With the telescope, you see all of the light together, but the spectrograph allows you to pick out different pieces; like this wavelength of light means that there is sodium, or this one means that there’s water.”

Previous observations of tau Boötis b with the VLT in Chile had identified carbon monoxide as well as cooler high-altitude temperatures in its atmosphere.

Now, with this proven IR RV technique, the atmospheres of exoplanets that don’t happen to cross in front of their stars from our point of view can also be scrutinized for the presence of water, as well as other interesting compounds.

“We now are applying our effective new infrared technique to several other non-transiting planets orbiting stars near the Sun,” said Chad Bender, a research associate in the Penn State Department of Astronomy and Astrophysics and a co-author of the paper. “These planets are much closer to us than the nearest transiting planets, but largely have been ignored by astronomers because directly measuring their atmospheres with previously existing techniques was difficult or impossible.”

Once the next generation of high-powered telescopes are up and running — like the James Webb Space Telescope, slated to launch in 2018 — even smaller and more distant exoplanets can be observed with the IR method… perhaps helping to make the groundbreaking discovery of a planet like ours.

“While the current state of the technique cannot detect earthlike planets around stars like the Sun, with Keck it should soon be possible to study the atmospheres of the so-called ‘super-Earth’ planets being discovered around nearby low-mass stars, many of which do not transit,” said Caltech professor of cosmochemistry and planetary sciences Geoffrey Blake. “Future telescopes such as the James Webb Space Telescope and the Thirty Meter Telescope (TMT) will enable us to examine much cooler planets that are more distant from their host stars and where liquid water is more likely to exist.”

The findings are described in a paper published in the February 24, 2014 online version of The Astrophysical Journal Letters.

Read more in this Caltech news article by Jessica Stoller-Conrad.

Sources: Caltech and EurekAlert press releases.

High Potential for Life Circling Alpha Centauri B, our Nearest Neighbor

While exoplanets make the news on an almost daily basis, one of the biggest announcements occurred in 2012 when astronomers claimed the discovery of an Earth-like planet circling our nearest neighbor, Alpha Centauri B, a mere 4.3 light-years away. That’s almost close enough to touch.

Of course such a discovery has led to a heated debate over the last three years. While most astronomers remain skeptical of this planet’s presence and astronomers continue to study this system, computer simulations from 2008 actually showed the possibility of 11 Earth-like planets in the habitable zone of Alpha Centauri B.

Now, recent research suggests that five of these computer-simulated planets have a high potential for photosynthetic life.

The 2008 study calculated the likely number of planets around Alpha Centauri B by assuming an initial protoplanetary disk populated with 400 – 900 rocks, or protoplanets, roughly the size of the Moon. They then tracked the disk over the course of 200 million years through n-body simulations — models of how objects gravitationally interact with one another over time — in order to determine the total number of planets that would form from the disk.

While the number and type of exoplanets depended heavily on the initial conditions given to the protoplanetary disk, the eight computer simulations predicted the formation of 21 planets, 11 of which resided within the habitable zone of the star.

A second team of astronomers, led by Dr. Antolin Gonzalez of the Universidad Central de Las Villas in Cuba, took these computer simulations one step further by assessing the likelihood these planets are habitable or even contain photosynthetic life.

The team used multiple measures that asses the potential for life. The Earth Similarity index “is a multi-parameter first assessment of Earth-likeness for extrasolar planets,” Dr. Gonzalez told Universe Today. It predicts (on a scale from zero to one with zero meaning no similarity and one being identical to Earth) how Earth-like a planet is based on its surface temperature, escape velocity, mean radius and bulk density.

Planets with an Earth Similar index from 0.8 – 1 are considered capable of hosting life similar to Earth’s. As an example Mars has an Earth Similar index in the range of 0.6 – 0.8. It is thus too low to support life today.

However, the Earth Similarity index alone is not an objective measure of habitability, Gonzalez said. It assumes the Earth is the only planet capable of supporting life. The team also relied on the P model for biological productivity, which takes into account the planet’s surface temperature and the amount of carbon dioxide present.

At this point in time “there is no way to predict, at least approximately, the partial pressure of carbon dioxide with the known data, or the variations from a planet to another,” Gonzalez said. Instead “we assumed a constant partial pressure of carbon dioxide for all planets simplifying the model to a function of temperature.”

Gonzalez’s team found that of the 11 computer-simulated planets in the habitable zone, five planets are prone for photosynthetic life. Their Earth Similarity index values are 0.92, 0.93, 0.87, 0.91 and 0.86. If we take into account their corresponding P model values we find that two of them have better conditions than Earth for life.

According to this highly theoretical paper: if there are planets circling our nearest neighbor, they’re likely to be teeming with life. It’s important to note that while these indexes may prove to be very valuable years down the road (when we have a handful of Earth-like planets to study), we are currently only looking for life as we know it.

The paper has been published in the Cuban journal: Revista Cubana de Fisica and is available for download here. For more information on Alpha Centauri Bb please read a paper available here published in the Astrophysical Journal.

Kepler Finds an Earth-Sized “Gas Giant”

Gas planets aren’t always bloated, monstrous worlds the size of Jupiter or Saturn (or larger) they can also apparently be just barely bigger than Earth. This was the discovery announced earlier today during the 223rd meeting of the American Astronomical Society in Washington, DC, when findings regarding the gassy (but surprisingly small) exoplanet KOI-314c were presented.

“This planet might have the same mass as Earth, but it is certainly not Earth-like,” said David Kipping of the Harvard-Smithsonian Center for Astrophysics (CfA), lead author of the discovery. “It proves that there is no clear dividing line between rocky worlds like Earth and fluffier planets like water worlds or gas giants.”

Discovered by the Kepler space telescope — ironically, during a hunt for exomoons — KOI-314c was found transiting a red dwarf star only 200 light-years away — “a stone’s throw by Kepler’s standards,” according to Kipping. (Kepler’s observation depth is about 3000 light-years.)

Relative size comparison of KOI-314c and Earth; both have similar mass. (J. Major)
Relative size comparison of KOI-314c and Earth; both have similar mass. (J. Major)

Kipping used a technique called transit timing variations (TTV) to study two of three exoplanets found orbiting KOI-314. Both are about 60% larger than Earth in diameter but their respective masses are very different. KOI-314b is a dense, rocky world four times the mass of Earth, while KOI-314c’s lighter, Earthlike mass indicates a planet with a thick “puffy” atmosphere… similar to what’s found on Neptune or Uranus.

Unlike those chilly worlds, though, this newfound exoplanet turns up the heat. Orbiting its star every 23 days, temperatures on KOI-314c reach 220ºF (104ºC)… too hot for water to exist in liquid form and thus too hot for life as we know it.

In fact Kipping’s team found KOI-314c to only be 30 percent denser than water, suggesting that it has a “significant atmosphere hundreds of miles thick,” likely composed of hydrogen and helium.

It’s thought that KOI-314c may have originally been a “mini-Neptune” gas planet and has since lost some of its atmosphere, boiled off by the star’s intense radiation.

Not only is KOI-314c the lightest exoplanet to have both its mass and diameter measured but it’s also a testament to the success and sensitivity of the relatively new TTV method, which is particularly useful in multiple-planet systems where the tiniest gravitational wobbles reveal the presence and details of neighboring bodies.

(Watch the latest Kepler Orrery video here)

“We are bringing transit timing variations to maturity,” Kipping said. He added during the closing remarks of his presentation at AAS223: “It’s actually recycling the way Neptune was discovered by watching Uranus’ wobbles 150 years ago. I think it’s a method you’ll be hearing more about. We may be able to detect even the first Earth 2.0 Earth-mass/Earth-radius using this technique in the future.”

Source: Harvard Smithsonian CfA press release

Prebiotic Molecules May Form in Exoplanet Atmospheres

Before there was life as we know it, there were molecules. And after many seemingly unlikely steps these molecules underwent a magnificent transition: they became complex systems with the capability to reproduce, pass along information and drive chemical reactions. But the host of steps leading up to this transition has remained one of science’s beloved mysteries.

New research suggests that the building blocks of life — prebiotic molecules — may form in the atmospheres of planets, where the dust provides a safe platform to form on and various reactions with the surrounding plasma provide enough energy necessary to create life.

“If the formation of life is like a jigsaw puzzle — a very big and complicated jigsaw puzzle — I like to imagine prebiotic molecules as some of the individual puzzle pieces,” said St. Andrews professor Dr. Craig Stark. “Putting the pieces together you form more complicated biological structures making a clearer, more recognizable picture. And when all the pieces are in place the resulting picture is life.”

We currently think prebiotic molecules form on the tiny ice grains in interstellar space. While this may seem to contradict the readily accepted belief that life in space is impossible, the surface of the grain actually provides a nice hospitable environment for life to form as it protects molecules from harmful space radiation.

“Molecules are formed on the dust surface from the adsorption of atoms and molecules from the surrounding gas,” Stark told Universe Today. “If the appropriate ingredients to make a particular molecular compound are available, and the conditions are right, you’re in business.”

By “conditions,” Stark is hinting at the second ingredient necessary: energy. The simple molecules that populate the galaxy are relatively stable; without an incredible amount of energy they won’t form new bonds. It has been thought that life could form in lightning strikes and volcanic eruptions for this very reason.

So Stark and his colleagues turned their eyes to the atmospheres of exoplanets, where dust is immersed in a plasma full of positive ions and negative electrons. Here the electrostatic interactions of dust particles with plasma may provide the high energy necessary to form prebiotic compounds.

In a plasma the dust grain will soak up the free electrons quickly, becoming negatively charged. This is because electrons are lighter, and therefore quicker, than positive ions. Once the dust grain is negatively charged it will attract a flux of positive ions, which will accelerate toward the dust particle and collide with more energy than they would in a neutral environment.

In order to test this, the authors studied an example atmosphere, which allowed them to examine the various processes that may turn the ionized gas into a plasma as well as determine if the plasma would lead to energetic enough reactions.

“As a proof of principle we looked at the sequence of chemical reactions that lead to the formation of the simplest amino acid glycine,” Stark said. Amino acids are great examples of prebiotic molecules because they are required for the formation of proteins, peptides and enzymes.

Their models showed that “the plasma ions can indeed be accelerated to sufficient energies that exceed the activation energies for the formation of formaldehyde, ammonia, hydrogen cyanide and ultimately the amino acid glycine,” Stark told Universe Today. “This may not have been possible if the plasma was absent.”

The authors demonstrated that with modest plasma temperatures, there is enough energy to form the prebiotic molecule glycine. Higher temperatures may also enable more complex reactions and therefore more intricate prebiotic molecules.

Stark and his colleagues demonstrated a viable pathway to the formation of a prebiotic molecule, and therefore life, in seemingly common conditions. While the origin of life may remain one of science’s beloved mysteries, we continue to gain a better understanding, one puzzle piece at a time.

The paper has been accepted for publication in the journal Astrobiology and is available for download here.

Rocky Earth-sized World is a ‘Sungrazing’ Exoplanet

A newly verified planet found in data from the Kepler mission delivers on the space telescope’s task of finding Earth-size planets around other stars. The new planet, called Kepler-78b, is the first Earth-sized exoplanet discovered that has a rocky composition like that of Earth. Similarities to Earth, however, end there. Kepler-78b whizzes around its host star every 8.5 hours at a distance of about 1.5 million kilometers, making it a blazing inferno and not suitable for life as we know it.

“We’ve been hearing about the sungrazing Comet ISON that will go very close to the Sun next month,” said Andrew Howard, of the University of Hawaii at Manoa’s Institute for Astronomy. “Comet ISON will approach the Sun about the same distance that Kepler-78b orbits its star, so this planet spends its entire life as a sungrazer.”

Howard is the lead author on one of two papers published in Nature that details the discovery of the new planet. He spoke during a media webcast discussing the finding.

“This is a planet that exists but shouldn’t,” added astronomer David Latham of the Harvard-Smithsonian Center for Astrophysics (CfA), also discussing the discovery during the webcast.

Kepler-78b is 1.2 times the size of Earth with a diameter of 14,800 km (9,200 miles) and 1.7 times more massive. As a result, astronomers say it has a density similar to Earth’s, which suggests an Earth-like composition of iron and rock. A handful of planets the size or mass of Earth have been discovered, but Kepler-78b is the first to have both a measured mass and size. With both quantities known, scientists can calculate a density and determine what the planet is made of.

Its star is slightly smaller and less massive than the sun and is located about 400 light-years from Earth in the constellation Cygnus.

However, the close-in orbit of Kepler-78b poses a challenge to theorists. According to current theories of planet formation, it couldn’t have formed so close to its star, nor could it have moved there. Back when this planetary system was forming, the young star was larger than it is now. As a result, the current orbit of Kepler-78b would have been inside the swollen star.

This diagram illustrates the tight orbit of Kepler-78b, which orbits its star every 8.5 hours at a distance of less than a million miles. It is only 2.7 stellar radii from the center of the star, or 1.7 stellar radii from the star's surface. David A. Aguilar (CfA)
This diagram illustrates the tight orbit of Kepler-78b, which orbits its star every 8.5 hours at a distance of less than a million miles. It is only 2.7 stellar radii from the center of the star, or 1.7 stellar radii from the star’s surface. David A. Aguilar (CfA)

“It couldn’t have formed in place because you can’t form a planet inside a star,” said team member Dimitar Sasselov, also from CfA. “It couldn’t have formed further out and migrated inward, because it would have migrated all the way into the star. This planet is an enigma.”

One idea, suggested Howard, is that the planet is the remnant core of a former gas giant planet, but that turns out to be a problem as well. “We just don’t know what the origin of this planet is,” Howard said.

However, the two teams of planet hunters feel that its existence bodes well for future discoveries of habitable planets.

The two independent research teams used ground-based telescopes for follow-up observations to confirm and characterize Kepler-78b. The team led by Howard used the W. M. Keck Observatory atop Mauna Kea in Hawaii. The other team led by Francesco Pepe from the University of Geneva, Switzerland, did their ground-based work at the Roque de los Muchachos Observatory on La Palma in the Canary Islands.

To determine the planet’s mass, the teams employed the radial velocity method to measure how much the gravitation tug of an orbiting planet causes its star to wobble. Kepler, on the other hand, determines the size or radius of a planet by the amount of starlight blocked when it passes in front of its host star.

“Determining mass of an Earth-sized planet is technically daunting,” Howard said during the webcast, explaining how they used the HIRES (High Resolution Echelle Spectrometer) on Keck. “We pushed HIRES to its limit. The observations were difficult because the star is young with many more star spots (just like sunspots on our Sun) than our Sun, and we have to remove them from our data. But since this planet orbits every eight and a half hours, we were able to watch an entire orbit in one night. We clearly saw the planet’s signal, and we watched it eight different nights.”

David Aguilar from CfA said both teams knew the other team was studying this star, but they didn’t compare their work until both teams were ready to submit their papers so that they wouldn’t influence each other. “It was very encouraging both teams got the same result,” Aguilar said.

Howard also thought having two separate teams work on the same target was great. “We didn’t have to wait for further confirmation of the planet, because the two teams confirmed each other,” he said. “In science, this is as good as it gets.”

Francesco Pepe from the second team said they benefitted from using a twin of the original HARPS (High Accuracy Radial velocity Planet Searcher) which has found nearly 200 exoplanets. “HARPS North at La Palma has the same precision and efficiency as its twin,” Pepe explained during the webcast, “and we decided to guarantee time to follow up on small exoplanet candidates from Kepler. We optimized our observing strategy and we expect many more confirmations in the coming years from this technique.”

As for Kepler-78b, this is a doomed world. Gravitational tides will continue to pull Kepler-78b even closer to its star. Eventually it will move so close that the star’s gravity will rip the world apart. Theorists predict that the planet will vanish within three billion years. Interestingly, astronomers say, our solar system could have held a planet like Kepler-78b. If it had, the planet would have been destroyed long ago leaving no signs for astronomers today.

“We did not detect additional planets in this system,” said Howard, “but we hope to observe this system more in the future.”

Paper by Howard et al.: A Rocky Composition for an Earth-sized Exoplanet

Paper by Pepe et al.: An Earth-sized planet with an Earth-like density

Additional info: CfA, NASA, MIT, Keck, Nature.

Is That Planet Habitable? Look To The Star First, New Study Cautions

Finding Earth 2.0, in the words of noted SETI researcher Jill Tarter, is something a lot of exoplanet searchers are hoping for one day. They’re trying not to narrow down their search to Sun-like stars, but also examine stars that are smaller, like red dwarfs.

A new study, however, cautions that the X-ray environment of these dwarfs may give us false positives. They looked at Earth-mass planets in the neighborhood of four stars, such as GJ 667 (which has three planets that could be habitable), and concluded it’s possible for oxygen to reside in these planets even in the absence of life.

The work builds on a published paper in the Astrophysical Journal that argues that GJ 876, studied by the Hubble Space Telescope, could allow a hypothetical planet to have plenty of oxygen in its atmosphere, even without the presence of life.

This artist's conception shows the newly discovered super-Earth GJ 1214b, which orbits a red dwarf star 40 light-years from our Earth. Credit: Credit: David A. Aguilar, CfA
This artist’s conception shows the newly discovered super-Earth GJ 1214b, which orbits a red dwarf star 40 light-years from our Earth. Credit: Credit: David A. Aguilar, CfA

The researchers themselves, however, caution that the results are preliminary and there is a lot more to study before coming to a definitive conclusion.

For example: “The effects of stellar flares on the atmosphere of the hypothetical Earth-like planet around GJ 876 have not been considered in this work,” stated Kevin France, who is with the University of Colorado at Boulder and also a co-author.

“At this point, we do not have a sufficient understanding of the amplitude and frequency of such flares on older, low-mass exoplanet host stars to make predictions about their impact on the production of biomarker signatures.”

The report was presented at the American Astronomical Society division for planetary sciences meeting in Denver today (Oct. 7). It was not immediately clear from a press release if the newer study has been submitted for peer review.

Source: AAS Division for Planetary Sciences

How Spitzer’s Focus Changed To Strange New Worlds

After 10 years in space — looking at so many galaxies and stars and other astronomy features — the Spitzer Space Telescope is being deployed for new work: searching for alien worlds.

The telescope is designed to peer in infrared light (see these examples!), the wavelength in which heat is visible. When looking at infrared light from exoplanets, Spitzer can figure out more about their atmospheric conditions. Over time, it can even detect brightness differences as the planet orbits its sun, or measure the temperature by looking at how much the brightness declines when the planet goes behind its star. Neat stuff overall.

“When Spitzer launched back in 2003, the idea that we would use it to study exoplanets was so crazy that no one considered it,” stated Sean Carey of NASA’s Spitzer Science Center, which is at the California Institute of Technology. “But now the exoplanet science work has become a cornerstone of what we do with the telescope.”

Of course, the telescope wasn’t designed to do this. But to paraphrase the movie Apollo 13, NASA was interested in what the telescope could do while it’s in space — especially because the planet-seeking Kepler space telescope has been sidelined by a reaction wheel problem. Redesigning Spitzer, in a sense, took three steps.

Classifying Galaxies
An example of Spitzer’s past work: This image from NASA’s Spitzer Space Telescope shows infrared light from the Sunflower galaxy, otherwise known as Messier 63. Spitzer’s view highlights the galaxy’s dusty spiral arms. Image credit: NASA/JPL-Caltech

Fixing the wobble: Spitzer is steady, but not so steady that it could easily pick out the small bit of light that an exoplanet emits. Engineers determined that the telescope actually wobbled regularly and would wobble for an hour. Looking into the problem further, they discovered it’s because a heater turns on to keep the telescope battery’s temperature regulated.

“The heater caused a strut between the star trackers and telescope to flex a bit, making the position of the telescope wobble compared to the stars being tracked,” NASA stated. In October 2010, NASA decided to cut the heating back to 30 minutes because the battery only needs about 50 per cent of the heat previously thought. Half the wobble and more exoplanets was more the recipe they were looking for.

The Spitzer Space Telescope.  Credit:  NASA
The Spitzer Space Telescope. Credit: NASA

Repurposing a camera: Spitzer has a pointing control reference sensor “peak-up” camera on board, which originally gathered up infrared light to funnel to a spectrometer. It also calibrated the telescope’s star-tracker pointing devices. The same principle was applied to infrared camera observations, putting stars in the center of camera pixels and allowing a better view.

Remapping a camera pixel: The scientists charted the variations in a single pixel of the camera that showed them which were the most stable areas for observations. For context, about 90% of Spitzer’s exoplanet observations are about a 1/4 of a pixel wide.

That’s pretty neat stuff considering that Spitzer’s original mission was just 2.5 years, when it had coolant on board to allow three temperature-sensitive science instruments to function. Since then, engineers have set up a passive cooling system that lets one set of infrared cameras keep working.

Source: NASA