An exoplanet transiting across the face of its star, demonstrating one of the methods used to find planets beyond our solar system. Credit: ESA/C. Carreau
With exoplanet discoveries coming at us several times a month, finding these worlds is a hot field of research. Once the planets are found and confirmed, however, there’s a lot more that has to be done to understand them. What are they made of? How habitable are they? What are their atmospheres like? These are questions we are only beginning to understand.
One long-standing exoplanet researcher argues that we don’t know very much about about alien planet atmospheres, as an example. Princeton University’s Adam Burrows says that not only is our understanding at an infancy, but the media and scientists overhype information based on very little data.
“Exoplanet research is in a period of productive fermentation that implies we’re doing something new that will indeed mature,” Burrows stated in a story posted on Princeton Journal Watch. “Our observations just aren’t yet of a quality that is good enough to draw the conclusions we want to draw.”
Artist’s conception of HD 189733 b, which may have winds that blow up to 22,000 mph (35,000 km/h). Credit: NASA
Burrow’s skepticism comes from how information on exoplanet atmospheres is collected. That uses a method called low-resolution photometry, which shows changes in light and radiation emitted from an object such as a planet. This could be affected by things such as a planet’s rotation and cloud cover.
Burrows’ solution is to use spectrometry, which can glean physical information through looking at light spectra, but that would be a challenge given the existing exoplanet-seeking infrastructure in space and on Earth uses telescopes that generally rely on other methods.
Artist's conception of exoplanet systems that could be observed by PLAnetary Transits and Oscillations of stars (PLATO), a European Space Agency telescope. Credit: ESA - C. Carreau
How could life arise in young solar systems? We’re still not sure of the answer on Earth, even for something as basic as if water arose natively on our planet or was carried in from other locations. Seeking answers to life’s beginnings will require eyes in the sky and on the ground looking for alien worlds like our own. And just yesterday, the European Space Agency announced it is going to add to that search.
The newly selected mission is called PLATO, for Planetary Transits and Oscillations. Like NASA’s Kepler space telescope, PLATO will scan the sky in search of stars that have small, periodic dips in their brightness that happen when planets go across their parent star’s face.
“The mission will address two key themes of Cosmic Vision: what are the conditions for planet formation and the emergence of life, and how does the solar system work,” stated ESA, referring to its plan for space science missions that extends from 2015 to 2025.
An exoplanet seen from its moon (artist’s impression). Via the IAU.
PLATO will operate far from Earth in a spot known as L2, a relatively stable Lagrange point about 1.5 million kilometers (930,000 miles) away from Earth in the opposite direction from the sun. Sitting there for at least six years, the observatory (which is actually made up of 34 small telescopes and cameras) will examine up to a million stars across half of the sky.
Find “statistically significant” Earth-mass planets in the habitable regions of several kinds of main-sequence stars;
Figure out the radius and mass of the star and any planets with 1% accuracy, and estimate the age of exoplanet systems with 10% accuracy;
Better determine the parameters of different kinds of planets, ranging from brown dwarfs (failed stars) to gas giants to rocky planets, all the way down to those that are smaller than Earth.
Artist’s impression of the deep blue planet HD 189733b, based on observations from the Hubble Space Telescope. Credit: NASA/ESA.
Adding PLATO’s observations to those telescopes on the ground that look at the radial velocity of planets, researchers will also be able to figure out each planet’s mass and radius (which then leads to density calculations, showing if it is made of rock, gas, or something else).
“The mission will identify and study thousands of exoplanetary systems, with an emphasis on discovering and characterising Earth-sized planets and super-Earths in the habitable zone of their parent star – the distance from the star where liquid surface water could exist,” ESA stated this week.
The telescope was selected from four competing proposals, which were EChO (the Exoplanet CHaracterisation Observatory), LOFT (the Large Observatory For x-ray Timing), MarcoPolo-R (to collect and return a sample from a near-Earth asteroid) and STE-Quest (Space-Time Explorer and QUantum Equivalence principle Space Test).
You can read more about PLATO at this website. It’s expected to launch from Kourou, French Guiana on a Soyuz rocket in 2024, with a budget of 600 million Euros ($822 million). And here’s more information on the Cosmic Vision and the two other M-class missions launching in future years, Euclid and Solar Orbiter.
Kepler space telescope's field of view. Credit: NASA
Astronomers estimate that the Milky Way contains up to 400 billion stars and thanks to the Kepler mission, we can now estimate that every star in our galaxy has on average 1.6 planets in orbit around it.
This new video from our friends Tony Darnell and Scott Lewis focuses on the discoveries that the Kepler Space Telescope has made, which has opened up a whole new universe and a new way of looking at stars as potential homes for other planets. Only about 20 years ago, we didn’t know if there were any other planets around any other stars besides our own. But now we know we live in a galaxy that contains more planets than stars.
If you extrapolate that number to the rest of the Universe, it’s mind-blowing. According to astronomers, there are probably more than 170 billion galaxies in the observable Universe, stretching out into a region of space 13.8 billion light-years away from us in all directions.
And so, if you multiply the number of stars in our galaxy by the number of galaxies in the Universe, you get approximately 1024 stars. That’s a 1 followed by twenty-four zeros, or a septillion stars.
However, it’s been calculated that the observable Universe is a bubble of space 47 billion years in all directions… or it could be much bigger, possibly infinite. It’s just that we can’t detect those stars because they’re outside the observable Universe.
So, there’s a lot of stars out there.
As the video says, space telescopes give us “a glimpse of our humble place in the cosmic ocean.”
A global map showing where all the volunteers are based. Image Credit: Zooniverse
Zooniverse — the renowned home of citizen science projects — is now one million strong. That’s one million registered volunteers since the project began less than seven years ago.
It all began when Galaxy Zoo launched in July 2007. The initial response to this project was overwhelming. Since then the Zooniverse team has created almost 30 citizen science projects ranging from astronomy to zoology.
“We are constantly amazed by the effort that the community puts into our projects,” said the Zooniverse team in an email regarding the news late last week.
Many projects have produced unique scientific results, ranging from individual discoveries to classifications that rely on input from thousands of volunteers. As of today there are 60+ papers listed on the websites publications page, many of which have made the news.
In the first two weeks after Galaxy Zoo’s launch, registered citizen scientists classified more than a million galaxies. Each volunteer was presented with an image from the Sloan Digital Sky Survey and asked to classifiy the galaxy as belonging to one of six categories: elliptical, clockwise spiral, anticlockwise spiral, edge-on, merger, or unsure.
An example of an unknown galaxy needing classification. Image credit: Galaxy Zoo
But citizen scientists weren’t simply labeling galaxies, they were helping astronomers to answer crucial questions and raise new ones about our current understandings of galaxy evolution. One significant finding showed that bar-shaped features in spiral galaxies has doubled over the latter half of the history of the Universe. This confirms that bars signify maturity in spiral galaxies and play an important role in shutting down star formation.
Another finding downplayed the importance of collisions in forming supermassive black holes. Citizen scientists found 13 bulgeless galaxies — suggesting they had never experienced a major collision — with supermassive black holes, nonetheless. All healthy black holes, with masses at least millions of times that of the Sun, must have grown through less dramatic processes.
Planet Hunters — a citizen science project developed in 2010 — has also seen wide success. Ordinary citizens examine the Kepler Space Telescope’s light curves of stars and flag any slight dips in brightness that might indicate a planet crossing in front of the star. Many eyes examine each light curve, allowing some to cross check others.
An example light curve asking for any obvious dips. Image Credit: Planet Hunters
In roughly three years, citizen scientists examined more than 19 million Kepler light curves. Contrary to what many astronomers expected, ordinary citizens were able to spot transiting objects that many computer algorithms missed.
In 2012, Planet Hunter volunteers, Kian Jek and Robert Gagliano discovered an exoplanet in a four-star system. The Neptune-size planet, labeled “Planet Hunters 1” (PH1), orbits its two parent stars every 138 days. A second pair of stars, approximately 90 billion miles away, are also gravitationally bound to the system. This wacky system was later confirmed by professional astronomers.
In 2013, Planet Hunter volunteers discovered yet another planet candidate, which, if confirmed, would make a known six-planet system really the first seven-planet system. The five innermost planets are smaller than Neptune, while the two outer planets are gas giants. All orbit within Earth’s orbit around the Sun.
These are only a few of Zooniverse’s citizen science projects. Others allow ordinary citizens to help analyze how whales communicate with one another, study the lives of the ancient Greeks, and even look at real life cancer data. So join today and become number one million and one.
Zooniverse is produced by the Citizen Science Alliance, which works with many academic and other partners worldwide.
Meet Kepler-22b, an exoplanet with an Earth-like radius in the habitable zone of its host star. Unfortunately its mass remains unknown. Image Credit: NASA
Astronomers constantly probe the skies for the unexpected. They search for unforeseen bumps in their data — signaling an unknown planet orbiting a star, a new class of astronomical objects or even a new set of physical laws that will rewrite the old ones. They are willing to embrace new ideas that may replace the wisdom of years past.
But there’s one exception to the rule: the search for Earth 2.0. Here we don’t want to find the unexpected, but the expected. We want to find a planet so similar to our own, we can almost call it home.
While, we can’t exactly image these planets with great enough detail to see if one’s a water world with luscious green plants and civilizations, we can use indirect methods to find an “Earth-like” planet — a planet with a similar mass and radius to the Earth.
There’s only one problem: the current techniques to measure an exoplanet’s mass are limited. To date astronomers measure radial velocity — tiny wobbles in a star’s orbit as it’s tugged by the gravitational pull of its exoplanet — to derive the planet-to-star mass ratio.
But given that most exoplanets are detected via their transit signal — dips in light as a planet passes in front of its host star — wouldn’t it be great if we could measure its mass based on this method alone? Well, astronomers at MIT have found a way.
Graduate student Julien de Wit and MacArthur Fellow Sara Seager have developed a new technique for determining mass by using an exoplanet’s transit signal alone. When a planet transits, the star’s light passes through a thin layer of the planet’s atmosphere, which absorbs certain wavelengths of the star’s light. Once the starlight reaches Earth it will be imprinted with the chemical fingerprints of the atmosphere’s composition.
The so-called transmission spectrum allows astronomers to study the atmospheres of these alien worlds.
But here’s the key: a more massive planet can hold on to a thicker atmosphere. So in theory, a planet’s mass could be measured based on the atmosphere, or the transmission spectrum alone.
Of course there isn’t a one to one correlation or we would have figured this out long ago. The atmosphere’s extent also depends on its temperature and the weight of its molecules. Hydrogen is so light it slips away from an atmosphere more easily than, say, oxygen.
So de Wit worked from a standard equation describing scale height — the vertical distance over which the pressure of an atmosphere decreases. The extent to which pressure drops off depends on the planet’s temperature, the planet’s gravitational force (a.k.a. mass) and the atmosphere’s density.
According to basic algebra: knowing any three of these parameters will let us solve for the fourth. Therefore the planet’s gravitational force, or mass, can be derived from its atmospheric temperature, pressure profile and density — parameters that may be obtained in a transmission spectrum alone.
With the theoretical work behind them, de Wit and Seager used the hot Jupiter HD 189733b, with an already well-established mass, as a case study. Their calculations revealed the same mass measurement (1.15 times the mass of Jupiter) as that obtained by radial velocity measurements.
This new technique will be able to characterize the mass of exoplanets based on their transit data alone. While hot Jupiters remain the main target for the new technique, de Wit and Seager aim to describe Earth-like planets in the near future. With the launch of the James Webb Space Telescope scheduled for 2018, astronomers should be able to obtain the mass of much smaller worlds.
The paper has been published in Science Magazine and is now available for download in a much longer form here.
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.
Diagram of Kepler-413b's unusual orbit around red and orange dwarf stars. Its orbit "wobbles" or precesses around the stars every 11 years. Credit: NASA, ESA, and A. Feild (STScI)
We’re lucky to live on a planet where it’s predictably warmer in the summer and colder in the winter in many regions, at least within a certain range. On Kepler-413b, it’s a world where you’d have to check the forecast more frequently, because its axis swings by a wild 30 degrees every 11 years. On Earth, by comparison, it takes 26,000 years to tilt by a somewhat lesser amount (23.5 degrees).
The exoplanet, which is 2,300 light-years away in the constellation Cygnus, orbits two dwarf stars — an orange one and a red one — every 66 days. While it would be fun to imagine a weather forecast on this planet, in reality it’s likely too hot for life (it’s close to its parent stars) and also huge, at 65 Earth-masses or a “super-Neptune.”
What’s even weirder is how hard it was to characterize the planet. Normally, astronomers spot these worlds either by watching them go across the face of their parent star(s), or by the gravitational wobbles they induce in those stars. The orbit, however, is tilted 2.5 degrees to the stars, which makes the transits far more unpredictable. It took several years of Kepler space telescope data to find a pattern.
“What we see in the Kepler data over 1,500 days is three transits in the first 180 days (one transit every 66 days), then we had 800 days with no transits at all,” stated Veselin Kostov, the principal investigator on the observation. “After that, we saw five more transits in a row,” added Kostov, who works both with the the Space Telescope Science Institute and Johns Hopkins University in Baltimore, Md.
It will be an astounding six years until the next transit happens in 2020, partly because of that wobble and partly because the stars have small diameters and aren’t exactly “edge-on” to our view from Earth. As for why this planet is behaving the way it does, no one is sure. Maybe other planets are messing with the orbit, or a third star is doing the same thing.
The next major question, the astronomers added, is if there are other planets out there like this that we just can’t see because of the gap between transit periods.
You can read more about this finding in The Astrophysical Journal (a Jan. 29 publication that doesn’t appear to be on the website yet) or in preprint version on Arxiv.
Artists impression of a Super-Earth, a class of planet that has many times the mass of Earth, but less than a Uranus or Neptune-sized planet. Credit: NASA/Ames/JPL-Caltech
Alien planets that are slightly bigger than Earth could be more life-friendly than exoplanets closer to our own size, a new study implies. These so-called “super-Earths” that are about two to three times that of our own planet could be “superhabitable” — implying that our own planet is a rare bird indeed when it comes to being good for life.
Bigger rocky planets would have a host of advantages, argue McMaster University’s Rene Heller and Weber State University’s John Armstrong in a paper recently published in Astrobiology. Among them: These worlds would have tectonic activity that takes longer to happen, meaning that the conditions would be more stable for life. Also, a bigger mass implies it’s easier to hang on to a thick atmosphere and to have “enhanced magnetic shielding” to hold a planet’s own against solar flares.
“Our argumentation can be understood as a refutation of the Rare Earth hypothesis. Ward and Brownlee (2000) claimed that the emergence of life required an extremely unlikely interplay of conditions on Earth, and they concluded that complex life would be a very unlikely phenomenon in the Universe,” stated the authors in their paper “Superhabitable Worlds.”
Information about Alpha Centauri Bb. Information about Alpha Centauri Bb. Credit: Planetary Habitability Laboratory/University of Puerto Rico/Arecibo
“While we agree that the occurrence of another truly Earth-like planet is trivially impossible, we hold that this argument does not constrain the emergence of other inhabited planets. We argue here in the opposite direction and claim that Earth could turn out to be a marginally habitable world. In our view, a variety of processes exists that can make environmental conditions on a planet or moon more benign to life than is the case on Earth.”
As a start, the scientists suggest looking at the Alpha Centauri system, where researchers in 2012 discovered a planet close to Earth’s size that is likely not habitable because it orbits so close to its sun.
The star system, however, is about the right age and has low enough radiation to allow life to occur on a planet or moon that “evolved similarly as it did on Earth”, providing the planet or moon “had the chance to collect water from comets and planetesimals beyond the snowline.” Further, it’s just four light-years from Earth, making it a good target for telescopic observations.
Artist's conception of Kepler 34b, which orbits two stars. Credit: David A. Aguilar (CfA)
Binary star systems are downright dangerous due to their complex gravitational interactions that can easily grind a planet to pieces. So how is it that we have found a few planets in these Tattooine-like environments?
Research led by the University of Bristol show that most planets formed far away from their central stars and then migrated in at some point in their history, according to research collected concerning Kepler-34b and other exoplanets.
The scientists did “computer simulations of the early stages of planet formation around the binary stars using a sophisticated model that calculates the effect of gravity and physical collisions on and between one million planetary building blocks,” stated the university.
“They found that the majority of these planets must have formed much further away from the central binary stars and then migrated to their current location.”
You can read more about the research in Astrophysical Journal Letters. It was led by Bristol graduate student Stefan Lines with participation from advanced research fellow and computational astrophysicst Zoe Lienhardt, among other collaborators.
A direct image of a brown dwarf companion (arrowed) taken at the Keck Observatory. (Credit: Crepp et al. 2014 APJ).
A recent find announced by astronomers may go a long ways towards understanding a crucial “missing link” between planets and stars.
The team, led by Friemann Assistant Professor of Physics at the University of Notre Dame’s Justin R. Crepp, recently released an image of a brown dwarf companion to a star 98 light years or 30 parsecs distant. This discovery marks the first time that a T-dwarf orbiting a Sun-like star with known radial velocity acceleration measurement has been directly imaged.
Located in the constellation Eridanus, the object weighs in at about 52 Jupiter masses, and orbits a 0.95 Sol mass star 51 Astronomical Units (AUs) distant once every 320-1900 years. Note that this wide discrepancy stems from the fact that even though we’ve been following the object for some 17 years since 1996, we’ve yet to ascertain whether we’ve caught it near apastron or periastron yet: we just haven’t been watching it long enough.
The T-dwarf, known as HD 19467 B, may become a benchmark in the study of sub-stellar mass objects that span the often murky bridge between true stars shining via nuclear fusion and ordinary high mass planets.
Brown dwarfs are classified as spectral classes M, L, T, and Y and are generally quoted as having a mass of between 13 to 80 Jupiters. Brown dwarfs utilize a portion of the proton-proton chain fusion reaction to create energy, known as deuterium burning. Low mass red dwarf stars have a mass range of 80 to 628 Jupiters or 0.75% to 60% the mass of our Sun. The Sun has just over 1,000 times Jupiter’s mass.
Researchers used data from the TaRgeting bENchmark-objects with Doppler Spectroscopy (TRENDS) high-contrast imaging survey, and backed it up with more precise measurements courtesy of the Keck observatory’s High-Resolution Echelle Spectrometer or HIRES instrument.
An artist’s conception of a T-type brown dwarf. (Credit: Tyrogthekreeper under a Wikimedia Commons Attribution-Share Alike 3.0 Unported license).
TRENDS uses adaptive optics, which relies on precise flexing the telescope mirror several thousands of times a second to compensate for the blurring effects of the atmosphere. Brown dwarfs shine mainly in the infrared, and objects such as HD 19467 B are hard to discern due to their close proximity to their host star. In this particular instance, for example, HD 19467 B was over 10,000 times fainter than its primary star, and located only a little over an arc second away.
“This object is old and cold and will ultimately garner much attention as one of the most well-studied and scrutinized brown dwarfs detected to date,” Crepp said in a recent Keck observatory press release. “With continued follow-up observations, we can use it as a laboratory to test theoretical atmospheric models. Eventually we want to directly image and acquire the spectrum of Earth-like planets. Then, from the spectrum, we should be able to tell what the planet is made of, what its mass is, radius, age, etc… basically all of its relevant properties.
Discovery of an Earth-sized exoplanet orbiting in a star’s habitable zone is currently the “holy grail” of exoplanet science. Direct observation also allows us to pin down those key factors, as well as obtain a spectrum of an exoplanet, where detection techniques such as radial velocity analysis only allow us to peg an upper mass limit on the unseen companion object.
This also means that several exoplanet candidates in the current tally of 1074 known worlds beyond our solar system also push into the lower end of the mass limit for substellar objects, and may in fact be low mass brown dwarfs as well.
Another key player in the discovery was the Near-Infrared Camera (second generation) or NIRC2. This camera works in concert with the adaptive optics system on the Keck II telescope to achieve images in the near infrared with a better resolution than Hubble at optical wavelengths, perfect for brown dwarf hunting. NIRC2 is most well known for its analysis of stellar regions near the supermassive black hole at the core of our galaxy, and has obtained some outstanding images of objects in our solar system as well.
The hexagonal primary mirror of the Keck II telescope. (Credit: SiOwl. A Wikimedia Commons image under a Creative Commons Attribution 3.0 Unported license).
What is the significance of the find? Free floating “rogue” brown dwarfs have been directly imaged before, such as the pair named WISE J104915.57-531906 which are 6.5 light years distant and were spotted last year. A lone 6.5 Jupiter mass exoplanet PSO J318.5-22 was also found last year by the PanSTARRS survey searching for brown dwarfs.
“This is the first directly imaged T-dwarf (very cold brown dwarf) for which we have dynamical information independent of its brightness and spectrum,” team lead researcher Justin Crepp told Universe Today.
Analysis of brown dwarfs is significant to exoplanet science as well.
“They serve as an essential link between our understanding of stars and planets,” Mr. Crepp said. “The colder, the better.”
And just as there has been a controversy over the past decade concerning “planethood” at the low end of the mass scale, we could easily see the debate applied to the higher end range, as objects are discovered that blur the line… perhaps, by the 23rd century, we’ll finally have a Star Trek-esque classifications scheme in place so that we can make statements such as “Captain, we’ve entered orbit around an M-class planet…”
Something that’s always been fascinating in terms of red and brown dwarf stars is also the possibility that a solitary brown dwarf closer to our solar system than Alpha Centauri could have thus far escaped detection. And no, Nibiru conspiracy theorists need not apply. Mr. Crepp notes that while possible, such an object is unlikely to have escaped detection by infrared surveys such as WISE. But what a discovery that’d be!
