Kepler Spots the First Exomoon Candidate 4000 Light Years From Earth

Ever since it was deployed in March of 2009, the Kepler mission has detected thousands of extra-solar planet candidates. In fact, between 2009 and 2012, it detected a total of 4,496 candidates, and confirmed the existence of 2,337 exoplanets. Even after two of its reaction wheels failed, the spacecraft still managed to turn up distant planets as part of its K2 mission, accounting for another 521 candidates and confirming 157.

However, according to a new study conducted by a pair of researches from Columbia University and a citizen scientist, Kepler may also have also found evidence of an extra-solar moon. After sifting through data from hundreds of transits detected by the Kepler mission, the researchers found one instance where a transiting planet showed signs of having a satellite.

Their study – which recently published online under the title “HEK VI: On the Dearth of Galilean Analogs in Kepler and the Exomoon Candidate Kepler-1625b I” – was by led Alex Teachey, a graduate student at Columbia University and a Graduate Research Fellow with the National Science Foundation (NSF). He was joined by David Kipping, an Assistant Professor of Astronomy at Columbia University and the Principal Investigator of The Hunt for Exomoons with Kepler (HEK) project, and Allan Schmitt, a citizen scientist.

Artist’s impression of NASA’s Kepler spacecraft. Credit: NASA

For years, Dr. Kipping has been searching the Kepler database for evidence of exomoons, as part of the HEK. This is not surprising, considering the kinds of opportunities that exomoons present for scientific research. Within our Solar System, the study of natural satellites has revealed important things about the mechanisms that drive early and late planet formation, and moons possess interesting geological features that are commonly found on other bodies.

It is for this reason that extending that research to the hunt for exoplanets is seen as necessary. Already, exoplanet-hunting missions like Kepler have turned up a wealth of planets that challenge conventional ideas about how planet formation and what kinds of planets are possible. The most noteworthy example are gas giants that have observed orbiting very close to their stars (aka. “Hot Jupiters”).

As such, the study of exomoons could yield valuable information about what kinds of satellites are possible, and whether or not our own moons are typical. As Teachey told Universe Today via email:

“Exomoons could tell us a lot about the formation of our Solar System, and other star systems. We see moons in our Solar System, but are they common elsewhere? We tend to think so, but we can’t know for sure until we actually see them. But it’s an important question because, if we find out there aren’t very many moons out there, it suggests maybe something unusual was going on in our Solar System in the early days, and that could have major implications for how life arose on the Earth. In other words, is the history of our Solar System common across the galaxy, or do we have a very unusual origin story? And what does that say about the chances of life arising here? Exomoons stand to offer us clues to answering these questions.”

A montage of some of the potentially-habitable moons in our Solar System. From top to bottom, left to right, these include Europa, Enceladus, TItan and Ceres. Credit: NASA/JPL

What’s more, many moons in the Solar System – including Europa, Ganymede, Enceladus and Titan – are thought to be potentially habitable. This is due to the fact that these bodies have steady supplies of volatiles (such as nitrogen, water, carbon dioxide, ammonia, hydrogen, methane and sulfur dioxide) and possess internal heating mechanisms that could provide the necessary energy to power biological processes.

Here too, the study of exomoons presents interesting possibilities, such as whether or not they may be habitable or even Earth-like. For these and other reasons, astronomers want to see if the planets that have been confirmed in distant star systems have systems of moons and what conditions are like on them. But as Teachey indicated, the search for exomoons presents a number of challenges compared to exoplanet-hunting:

“Moons are difficult to find because 1) we expect them to be quite small most of the time, meaning the transit signal will be quite weak to begin with, and 2) every time a planet transits, the moon will show up in a different place. This makes them more difficult to detect in the data, and modeling the transit events is significantly more computationally expensive. But our work leverages the moons showing up in different places by taking the time-averaged signal across many different transit events, and even across many different exoplanetary systems. If the moons are there, they will in effect carve out a signal on either side of the planetary transit over time. Then it’s a matter of modeling this signal and understanding what it means in terms of moon size and occurrence rate.”

To locate signs of exomoons, Teachey and his colleagues searched through the Kepler database and analyzed the transits of 284 exoplanet candidates in front of their respective stars. These planets ranged in size from being Earth-like to Jupiter-like in diameter, and orbited their stars at a distance of between ~0.1 to 1.0 AU. They then modeled the light curve of the stars using the techniques of phase-folding and stacking.

An artist’s conception of a habitable exomoon. Credit: NASA

These techniques are commonly used by astronomers who monitor stars for dips in luminosity that are caused by the transits of planets (i.e. the transit method). As Teachey explained, the process is quite similar:

“Basically we cut up the time-series data into equal pieces, each piece having one transit of the planet in the middle. And when we stack these pieces together we’re able to get a clearer picture of what the transit looks like… For the moon search we do essentially the same thing, only now we’re looking at the data outside the main planetary transit. Once we stack the data, we take the average values of all the data points within a certain time window and, if a moon is present, we ought to see some missing starlight there, which allows us to deduce its presence.”

What they found was a single candidate located in the Kepler-1625 system, a yellow star located about 4000 light years from Earth. Designated Kepler-1625B I, this moon orbits the large gas giant that is located within the star’s habitable zone, is 5.9 to 11.67 times the size of Earth, and orbits its star with a period of 287.4 days. This exomoon candidate, if it should be confirmed, will be the first exomoon ever discovered

The team’s results (which await peer review) also demonstrated that large moons to be a rare occurrence in the inner regions of star systems (within 1 AU). This was something of a surprise, though Teachey acknowledges that it is consistent with recent theoretical work. According to what some recent studies suggest, large planets like Jupiter could lose their moons as they migrate inward.

If this should prove to be the case, then what Teachey and his colleagues witnessed could be seen as evidence of that process. It could also be an indication our current exoplanet-hunting missions may not be up to the task of detecting exomoons. In the coming years, next-generations missions are expected to provide more detailed analyses of distant stars and their planetary systems.

An artist’s conception of a distance exomoon blocking out a star’s light. Credit: Dan

However, as Teachey indicated, these too could be limited in terms of what they can detect, and new strategies may ultimately be needed:

“The rarity of moons in the inner regions of these star systems suggests that individual moons will remain difficult to find in the Kepler data, and upcoming missions like TESS, which should find lots of very short period planets, will also have a difficult time finding these moons. It’s likely the moons, which we still expect to be out there somewhere, reside in the outer regions of these star systems, much as they do in our Solar System. But these regions are much more difficult to probe, so we will have to get even more clever about how we look for these worlds with present and near-future datasets.”

In the meantime, we can certainly be exited about the fact that the first exomoon appears to have been discovered. While these results await peer review, confirmation of this moon will mean additional research opportunities for Kepler-1625 system. The fact that this moon orbits within the star’s habitable zone is also an interesting feature, though its not likely the moon itself is habitable.

Still, the possibility of a habitable moon orbiting a gas giant is certainly interesting. Does that sound like something that might have come up in some science fiction movies?

Further Reading: arXiv

Earth-Sized Planet Takes Just Four Hours to Orbit its Star

The Kepler space observatory has made some interesting finds since it began its mission back in March of 2009. Even after the mission suffered the loss of two reaction wheels, it has continued to make discoveries as part of its K2 mission. All told, the Kepler and K2 missions have detected a total of 5,106 planetary candidates, and confirmed the existence of 2,493 planets.

One of the latest finds made using Kepler is EPIC 228813918 b, a terrestrial (i.e. rocky) planet that orbits a red dwarf star some 264 to 355 light years from Earth. This discovery raises some interesting questions, as it is the second time that a planet with an ultra-short orbital period – it completes a single orbit in just 4 hours and 20 minutes – has been found orbiting a red dwarf star.

The study, which was recently published online, was conducted by an international team of scientists who hail from institutions ranging from the Massachusetts Institute of Technology (MIT), the California Institute of Technology (Caltech), the Tokyo Institute of Technology, and the Institute of Astrophysics of the Canary Islands (IAC) to observatories and universities from all around the world.

NASA’s Kepler space telescope was the first agency mission capable of detecting Earth-size planets. Credit: NASA/Wendy Stenzel

As the team indicated in their study, the detection of this exoplanet was made thanks to data collected by numerous instruments. This included spectrographic data from the 8.2-m Subaru telescope and the 10-m Keck I telescope (both of which are located on Mauna Kea, Hawaii) and the Nordic Optical Telescope (NOT) at the Roque de los Muchachos Observatory in La Palma, Spain.

This was combined with speckle imaging from the 3.5-m WIYN telescope at the Kitt Peak National Observatory in Arizona, photometry from the NASA’s K2 mission, and archival information of the star that goes back over 60 years. After eliminating any other possible explanations – such as an eclipsing binary (EB) – they not only confirmed the orbital period of the planet, but also provided constrains on its mass and size. As they wrote:

“Using a combination of archival images, AO imaging, RV measurements, and light curve modelling, we show that no plausible eclipsing binary scenario can explain the K2 light curve, and thus confirm the planetary nature of the system. The planet, whose radius we determine to be 0.89 ± 0.09 [Earth radii], and which must have a iron mass fraction greater than 0.45, orbits a star of mass 0.463 ± 0.052 M and radius 0.442 ± 0.044 R.”
This orbital period – four hours and 20 minutes – is the second shortest of any exoplanet discovered to date, being just 4 minutes longer than that of KOI 1843.03, which also orbits an M-type (red dwarf) star. It is also the latest in a long line of recently-discovered exoplanets that complete a single orbit of their stars in less than a day. Planets belonging to this group are known as ultra-short-period (USP) planets, of which Kepler has found a total of 106.
Archival images of the star EPIC 228813918, demonstrating its proper motion over nearly six decades – from (i) 1954, (ii) 1992, and (iii) 2012. Credit: Smith et al.

However, what is perhaps most surprising about this find is just how massive it is. Though they didn’t measure the planet’s mass directly, their constraints indicate that the exoplanet has an upper mass limit of 0.7 Jupiter masses – which works out to over 222 Earth masses. And yet, the planet manages to pack this gas giant-like mass into a radius that is 0.80 to 0.98 times that of Earth.

The reason for this, they indicate, has to do with the planet’s apparent composition, which is particularly metal-rich:

“This leads to a constraint on the composition, assuming an iron core and a silicate mantle. We determine the minimum iron mass fraction to be 0.525 ± 0.075 (cf. 0.7 for KOI 1843.03), which is greater than that of Earth, Venus or Mars, but smaller than that of Mercury (approximately 0.38, 0.35, 0.26, and 0.68, respectively; Reynolds & Summers 1969).”

Ultimately, the discovery of this planet is significant for a number of reasons. On the one hand, the team indicated that the constraints their study placed on the planet’s composition could prove useful in helping to understand how our own Solar planets came to be.

“Discovering and characterizing extreme systems, such as USP planets like EPIC 228813918 b, is important as they offer constraints for planet formation theories,” they conclude. “Furthermore, they allow us to begin to constrain their interior structure – and potentially that of longer-period planets too, if they are shown to be a single population of objects.”

An artist’s depiction of extra-solar planets transiting an M-type (red dwarf) star. Credit: NASA/ESA/STScl

On the other hand, the study raises some interesting questions about USP planets – for instance, why the two shortest-period planets were both found orbiting red dwarf stars. A possible explanations, they claim, is that short-period planets could have longer lifetimes around M-dwarfs since their orbital decay would likely be much slower. However, they are quick to caution against making any tentative conclusions before more research is conducted.

In the future, the team hopes to conduct measurements of the planet’s mass using the radial velocity method. This would likely involve a next-generation high-resolution spectrograph, like the Infrared Doppler (IFD) instrument or the CARMENES instrument – which are currently being built for the Subaru Telescope and the Calar Alto Observatory (respectively) to assist in the hunt for exoplanets around red dwarf stars.

One thing is clear though. This latest find is just another indication that red dwarf stars are where exoplanet-hunters will need to be focusing their efforts in the coming years and decades. These low mass, ultra-cool and low-luminosity stars are where some of the most interesting and extreme finds are being made. And what we stand to learn by studying them promises to be most profound!

Further Reading: arXiv

NASA Announces 10, That’s Right 10! New Planets in Their Star’s Habitable Zone

The Kepler space telescope is surely the gift that keeps on giving. After being deployed in 2009, it went on to detect a total of 2,335 confirmed exoplanets and 582 multi-planet systems. Even after two of its reaction wheels failed, it carried on with its K2 mission, which has discovered an additional 520 candidates, 148 of which have been confirmed. And with yet another extension, which will last beyond 2018, it shows no signs of stopping!

In the most recent catalog to be released by the Kepler mission, an additional 219 new planet candidates have been added to its database. More significantly, 10 of these planets were found to be terrestrial (i.e. rocky), of comparable in size to Earth and orbited within their star’s habitable zone – the distance where surface temperatures would be warm enough to support liquid water.

These findings were presented at a news conference on Monday, June 19th, at NASA’s Ames Research Center. Of all the catalogs of Kepler candidates that have been released to date, this one is the most comprehensive and detailed. The eighth in a series of Kepler exoplanet catalogs, this one is based on data that was obtained from the first four years of the mission and is the final catalog that covers the spacecraft’s observations of the Cygnus constellation.

 Credits: NASA/Wendy Stenzel

Since 2014, Kepler has ceased looking at a set starfield in the Cygnus constellation and has been collecting data on its second mission – observing fields on the plane of the ecliptic of the Milky Way Galaxy. With the release of this catalog, there are now 4,034 planet candidates that have been identified by Kepler – of which 2,335 have been verified.

An important aspect of this catalog were the methods that were used for producing it, which were the most sophisticated to date. As with all planets detected by Kepler, the latest finds were all made using the transit method. This consists of monitoring stars for occasional dips in brightness, which is used to confirm the presence of planets transiting between the star and the observer.

To ensure that the detections in this latest catalog were real, the team relied on two approaches to eliminate false positives. This consisted of introducing simulated transits into the dataset to make sure the dips that Kepler detected were consistent with planets. Then, they added false signals to see how often the analysis mistook these for planet transits. From this, they were able to tell which planets were overcounted and which were undercounted.

This led to another exciting find, which was the indication that for all of the smaller exoplanets discovered by Kepler, most fell within one of two distinct groupings. Essentially, half the planets that we know of in the galaxy are either rocky in nature and larger than Earth (i.e. Super-Earth’s), or are gas giants that are comparable in size to Neptune (i.e. smaller gas giants).

This conclusion was reached by a team of researchers who used the W.M. Keck Observatory to measure the sizes of 1,300 stars in the Kepler field of view. From this, they were able to determine the radii of 2,000 Kepler planets with extreme precision, and found that there was a clear division between rocky, Earth-sized planets and gaseous planets smaller than Neptune – with few in between.

As Benjamin Fulton, a doctoral candidate at the University of Hawaii in Manoa and the lead author of this study, explained:

“We like to think of this study as classifying planets in the same way that biologists identify new species of animals. Finding two distinct groups of exoplanets is like discovering mammals and lizards make up distinct branches of a family tree.”

These results are sure to have drastic implications when it comes to knowing the frequency of different types of planets in our galaxy, as well as the study of planet formation. For instance, they noted that most rocky planets discovered by Kepler are up to 75% larger than Earth. And for reasons that are not yet clear, about half of them take on hydrogen and helium, which swells their size to the point that they become almost Neptune-sized.

Histogram shows the number of planets per 100 stars as a function of planet size relative to Earth. Credits: NASA/Ames Research Center/CalTech/University of Hawaii/B.J. Fulton

These findings could similarly have significant implications in the search for habitable planets and extra-terrestrial life. As Mario Perez, Kepler program scientist in the Astrophysics Division of NASA’s Science Mission Directorate, said during the presentation:

“The Kepler data set is unique, as it is the only one containing a population of these near Earth-analogs – planets with roughly the same size and orbit as Earth. Understanding their frequency in the galaxy will help inform the design of future NASA missions to directly image another Earth.”

From this information, scientists will be able to know with a greater degree of certainty just how many “Earth-like” planets exist within our galaxy. The most recent estimates place the number of planets in the Milky Way at about 100 billion. And based on this data, it would seem that many of these are similar in composition to Earth, albeit larger.

Combined with a statistical models of how many of these can be found within a circumstellar habitable zone, we should have a better idea of just how many potentially-life-bearing worlds are out there. If nothing else, this should simplify some of the math in the Drake Equation!

In the meantime, the Kepler space telescope will continue to make observations of nearby star systems in order to learn more about their exoplanets. This includes the TRAPPIST-1 system and its seven Earth-sized, rocky planets. Its a safe bet that before it is finally retired after 2018, it will have some more surprises in store for us!

Further Reading: NASA, NASA Kepler and K2

We Have More Details on the Outermost Trappist-1 Planet!

The announcement of a seven-planet system around the star TRAPPIST-1 earlier this year set off a flurry of scientific interest. Not only was this one of the largest batches of planets to be discovered around a single star, the fact that all seven were shown to be terrestrial (rocky) in nature was highly encouraging. Even more encouraging was the fact that three of these planets were found to be orbiting with the star’s habitable zone.

Since that time, astronomers have been seeking to learn all they can about this system of planets. Aside from whether or not they have atmospheres, astronomers are also looking to learn more about their orbits and surface conditions. Thanks to the efforts of a University of Washington-led international team of astronomers, we now have an accurate idea of what conditions might be like on its outermost planet – TRAPPIST-1h.

Continue reading “We Have More Details on the Outermost Trappist-1 Planet!”

Could Garnet Planets be Habitable?

The hunt for exoplanet has revealed some very interesting things about our Universe. In addition to the many gas giants and “Super-Jupiters” discovered by mission like Kepler, there have also been the many exoplanet candidate that comparable in size and structure to Earth. But while these bodies may be terrestrial (i.e. composed of minerals and rocky material) this does not mean that they are “Earth-like”.

For example, what kind of minerals go into a rocky planet? And what could these particular compositions mean for the planet’s geological activity, which is intrinsic to planetary evolution? According to new study produced by a team of astronomers and geophysicists, the composition of an exoplanet depends on the chemical composition of its star – which can have serious implications for its habitability.

The findings of this study were presented at the 229th Meeting of the American Astronomical Society (AAS), which will be taking place from Jan. 3rd to Jan. 7th. During an afternoon presentation – titled “Between a Rock and a Hard Place: Can Garnet Planets Be Habitable?” – Johanna Teske (an astronomer from the Carnegie Institute of Science)  showed how different types of stars can produce vastly different types of planets.

The Apache Point Observatory Galactic Evolution Experiment (APOGEE), which collects spectrographic information on distant stars. Credit: astronomy.as.virginia.edu

Using the Apache Point Observatory Galactic Evolution Experiment (APOGEE), which is part of the Sloan Digital Sky Survey (SDSS) Telescope at Apache Point Observatory, they examined spectrographic information obtained from 90 star systems – which were also observed by the Kepler Mission. These systems are of particular interest to exoplanet hunters because they have been shown to contain rocky planets.

As Teske explained during the course of the presentation, this information could help scientists to place further constraints on what it takes for a planet to be habitable. “[O]ur study combines new observations of stars with new models of planetary interiors,” she said. “We want to better understand the diversity of small, rocky exoplanet composition and structure — how likely are they to have plate tectonics or magnetic fields?”

Focusing on two star systems in particular – Kepler 102 and Kepler 407 – Teske demonstrated how the composition of a planet has a great deal to do with the composition of its star. Whereas Kepler 102 has five known planets, Kepler 407, has two different planets – one gaseous and the other terrestrial. And while Kepler 102 is quite similar to our Sun (slightly less luminous), Kepler 407 has close to the same mass (but a lot more silicon).

In order to understand what consequences these differences could have for planetary formation, the SDSS team turned to a team of geophysicists. Led by Cayman Unterborn from Arizona State University, this team ran computer models to see what kinds of planets each system would have. As Unterborn explained:

“We took the star compositions found by APOGEE and modeled how the elements condensed into planets in our models. We found that the planet around Kepler 407, which we called ‘Janet,” would likely be rich in the mineral garnet. The planet around Kepler 102, which we called ‘Olive,’ is probably rich in olivine, like Earth.”

Artist rendition of interior compositions of planets around the stars Kepler 102 and Kepler 407. Credit: Robin Dienel/Carnegie DTM

This difference would have considerable impact on planetary tectonics. For one, garnet is lot more rigid than olivine, which would mean “Janet” would experience less in the way of long-term plate tectonics. This in turn would mean that processes that are believed to be essential to life on Earth – like volcanic activity, atmospheric recycling, and mineral exchanges between the crust and mantle – would be less common.

This raises additional questions about the habitability of “Earth-like” planets in other star systems. In addition to being rocky and having strong magnetic fields and viable atmospheres, it seems that exoplanets also need to have the right mix of minerals in order to support life – life as we know it, at any rate. What’s more, this kind of research also helps us to understand how life came to emerge on Earth in the first place.

Looking forward, the research team hopes to extend their study to include all the 200,000 stars surveyed by APOGEE to see which could host terrestrial planets. This will allow astronomers to determine the mineral composition of more rocky worlds, thus helping them to determine which rocky exoplanets are “Earth-like”, and which are just “Earth-sized”.

Further Reading: SDSS

This Star Is The Roundest Natural Object Ever Seen

At one time, scientists believed that the Earth, the Moon, and all the other planets in our Solar System were perfect spheres. The same held true for the Sun, which they considered to be the heavenly orb that was the source of all our warmth and energy. But as time and research showed, the Sun is far from perfect. In addition to sunspots and solar flares, the Sun is not completely spherical.

For some time, astronomers believed this was the case with other stars as well. Owing to a number of factors, all stars previously studied by astronomers appeared to experience some bulging at the equator (i.e. oblateness). However, in a study published by a team of international astronomers, it now appears that a slowly rotating star located 5000 light years away is as close to spherical as we’ve ever seen!

Until now, observation of stars has been confined to only a few of the fastest-rotating nearby stars, and was only possible through interferometry. This technique, which is typically used by astronomers to obtain stellar size estimates, relies on multiple small telescopes obtaining electromagnetic readings on a star. This information is then combined to create a higher-resolution image that would be obtained by a large telescope.

Artist's impression of a white dwarf star in orbit around Sirius (a white supergiant). Credit: NASA, ESA and G. Bacon (STScI)
Artist’s impression of a Sirius, an A-type Main Sequence White star. Credit: NASA, ESA and G. Bacon (STScI)

However, by conducting asteroseismic measurements of a nearby star, a team of astronomers – from the Max Planck Institute, the University of Tokyo, and New York University Abu Dhabi (NYUAD) – were able to get a much more precise idea of its shape. Their results were published in a study titled “Shape of a Slowly Rotating Star Measured by Asteroseismology“, which recently appeared in the American Association for the Advancement of Science.

Laurent Gizon, a researcher with the Max Planck Institute, was the lead authjor on the paper. As he explained their research methodology to Universe Today via email:

“The new method that we propose in this paper to measure stellar shapes, asteroseismology, can be several orders of magnitude more precise than optical interferometry. It applies only to stars that oscillate in long-lived non-radial modes. The ultimate precision of the method is given by the precision on the measurement of the frequencies of the modes of oscillation. The longer the observation duration (four years in the case of Kepler), the better the precision on the mode frequencies. In the case of  KIC 11145123 the most precise mode frequencies can be determined to one part in 10,000,000. Hence the astonishing precision of asteroseismology.”

Located 5000 light years away from Earth, KIC 11145123 was considered a perfect candidate for this method. For one, Kepler 11145123 is a hot and luminous, over twice the size of our Sun, and rotates with a period of 100 days. Its oscillations are also long-lived, and correspond directly to fluctuations in its brightness. Using data obtained by NASA’s Kepler mission over a more than four year period, the team was able to get very accurate shape estimates.

The variations in brightness can be interpreted as vibrations, or oscillations within the stars, using a technique called asteroseismology. The oscillations reveal information about the internal structure of the stars, in much the same way that seismologists use earthquakes to probe the Earth's interior. Credit: Kepler Astroseismology team.
The variations in brightness can be interpreted as vibrations, or oscillations within the stars, using a technique called asteroseismology. Credit: Kepler Astroseismology team.

“We compared the frequencies of the modes of oscillation that are more sensitive to the low-latitude regions of the star to the frequencies of the modes that are more sensitive to higher latitudes,” said Gizon. “This comparison showed that the difference in radius between the equator and the poles is only 3 km with a precision of 1 km. This makes Kepler 11145123 the roundest natural object ever measured, it is even more round than the Sun.”

For comparison, our Sun has a rotational period of about 25 days, and the difference between its polar and equatorial radii is about 10 km. And on Earth, which has a rotational period of less than a day (23 hours 56 minutes and 4.1 seconds), there is a difference of over 23 km (14.3 miles) between its polar and equator. The reason for this considerable difference is something of a mystery.

In the past, astronomers have found that the shape of a star can come down to multiple factors – such as their rotational velocity, magnetic fields, thermal asphericities, large-scale flows, strong stellar winds, or the gravitational influence of stellar companions or giant planets. Ergo, measuring the “asphericity” (i.e. the degree to which a star is NOT a sphere) can tell astronomers much about the star structures and its system of planets.

Ordinarily, rotational velocity has been seen to have a direct bearing on the stars asphericity – i.e. the faster it rotates, the more oblate it is. However, when looking at data obtained by the Kepler probe over a period of four years, they noticed that its oblateness was only a third of what they expected, given its rotational velocity.

Laurent Gizon, the lead researcher of the study, pictured comparing images of our Sun and Kepler 11145123. Credit: Max Planck Institute for Solar System Research, Germany.
Laurent Gizon, the lead researcher of the study, pictured with asteroseismic readings of Kepler 11145123. Credit: Max Planck Institute for Solar System Research, Germany.

As such, they were forced to conclude that something else was responsible for the star’s highly spherical shape. “”We propose that the presence of a magnetic field at low latitudes could make the star look more spherical to the stellar oscillations,” said Gizon. “It is known in solar physics that acoustic waves propagate faster in magnetic regions.”

Looking to the future, Gizon and his colleagues hope to examine other stars like Kepler 11145123. In our Galaxy alone, there are many stars who’s oscillations can be accurately measured by observing changes in their brightness. As such, the international team hopes to apply their asteroseismology method to other stars observed by Kepler, as well as upcoming missions like TESS and PLATO.

“Just like helioseismology can be used to study the Sun’s magnetic field, asteroseismology can be used to study magnetism on distant stars,” Gizon added. “This is the main message of this study.”

Further Reading: ScienceMag, Max Planck Institute

Tabby’s Star Megastructure Mystery Continues To Intrigue

Last fall, astronomers were surprised when the Kepler mission reported some anomalous readings from KIC 8462852 (aka. Tabby’s Star). After noticing a strange and sudden drop in brightness, speculation began as to what could be causing it – with some going so far as to suggest that it was an alien megastructure. Naturally, the speculation didn’t last long, as further observations revealed no signs of intelligent life or artificial structures.

But the mystery of the strange dimming has not gone away. What’s more, in a paper posted this past Friday to arXiv, Benjamin T. Montet and Joshua D. Simon (astronomers from the Cahill Center for Astronomy and Astrophysics at Caltech and the Carnegie Institute of Science, respectively) have shown how an analysis of the star’s long-term behavior has only deepened the mystery further.

To recap, dips in brightness are quite common when observing distant stars. In fact, this is one of the primary techniques employed by the Kepler mission and other telescopes to determine if planets are orbiting a star (known as Transit Method). However, the “light curve” of Tabby’s Star – named after the lead author of the study that first detailed the phenomena (Tabetha S. Boyajian) – was particularly pronounced and unusual.

Freeman Dyson theorized that eventually, a civilization would be able to build a megastructure around its star to capture all its energy. Credit: SentientDevelopments.com
Freeman Dyson theorized that eventually, a civilization would be able to build a megastructure around its star to capture all its energy. Credit: SentientDevelopments.com

According to the study, the star would experience a ~20% dip in brightness, which would last for between 5 and 80 days. This was not consistent with a transitting planet, and Boyajian and her colleagues hypothesized that it was due to a swarm of cold, dusty comet fragments in a highly eccentric orbit accounted for the dimming.

However, others speculated that it could be the result of an alien megastructure known as Dyson Sphere (or Swarm), a series of structures that encompass a star in whole or in part. However, the SETI Institute quickly weighed in and indicated that radio reconnaissance of KIC 8462852 found no evidence of technology-related radio signals from the star.

Other suggestions were made as well, but as Dr. Simon of the Carnegie Institute of Science explained via email, they fell short. “Because the brief dimming events identified by Boyajian et al. were unprecedented, they sparked a wide range of ideas to explain them,” he said. “So far, none of the proposals have been very compelling – in general, they can explain some of the behavior of KIC 8462852, but not all of it.”

To put the observations made last Fall into a larger context, Montet and Simon decided to examine the full-frame photometeric images of KIC 8462852 obtained by Kepler over the last four years.  What they found was that the total brightness of the star had been diminishing quite astonishingly during that time, a fact which only deepens the mystery of the star’s light curve.

Photometry of KIC8462852 as measured by Kepler data. The analysis reveals a slow but steady decrease in the star’s luminosity for about 1000 days, followed by a period of more rapid decline. Credit: Montet & Simon 2016
Photometry of KIC8462852 obtained by the Kepler mission, showing a period of more rapid decline during the later period of observation. Credit: Montet & Simon 2016

As Dr. Montet told Universe Today via email:

“Every 30 minutes, Kepler measures the brightness of 160,000 stars in its field of view (100 square degrees, or approximately as big as your hand at arm’s length). The Kepler data processing pipeline intentionally removes long-term trends, because they are hard to separate from instrumental effects and they make the search for planets harder. Once a month though, they download the full frame, so the brightness of every object in the field can be measured. From this data, we can separate the instrumental effects from astrophysical effects by seeing how the brightness of any particular star changes relative to all its neighboring stars.”

Specifically, they found that over the course of the first 1000 days of observation, the star experienced a relatively consistent drop in brightness of 0.341% ± 0.041%, which worked out to a total dimming of 0.9%. However, during the next 200 days, the star dimmed much more rapidly, with its total stellar flux dropping by more than 2%.

For the final 200 days, the star’s magnitude once again consistent and similar to what it was during the first 1000 – roughly equivalent to 0.341%. What is impressive about this is the highly anomalous nature of it, and how it only makes the star seem stranger. As Simon put it:

“Our results show that over the four years KIC 8462852 was observed by Kepler, it steadily dimmed.  For the first 2.7 years of the Kepler mission the star faded by about 0.9%.  Its brightness then decreased much faster for the next six months, declining by almost 2.5% more, for a total brightness change of around 3%.  We haven’t yet found any other Kepler stars that faded by that much over the four-year mission, or that decreased by 2.5% in six months.”

Artist's conception of the Kepler Space Telescope. Credit: NASA/JPL-Caltech
Artist’s conception of the Kepler Space Telescope. Credit: NASA/JPL-Caltech

Of the over 150,000 stars monitored by the Kepler mission, Tabby’s Starr is the only one known to exhibit this type of behavior. In addition, Monetet and Cahill compared the results they obtained to data from 193 nearby stars that had been observed by Kepler, as well as data obtained on 355 stars with similar stellar parameters.

From this rather large sampling, they found that a 0.6% change in luminosity over a four year period – which worked out to about 0.341% per year – was quite common. But none ever experienced the rapid decline of more than 2% that KIC 8462852 experienced during that 200 days interval, or the cumulative fading of 3% that it experienced overall.

Montet and Cahill looked for possible explanations, considering whether the rapid decline could be caused by a cloud of transiting circumstellar material. But whereas some phenomena can explain the long-term trend, and other the short-term trend, no one explanation can account for it all. As Montet explained:

“We propose in our paper that a cloud of gas and dust from the remnants of a planetesimal after a collision in the outer solar system of this star could explain the 2.5% dip of the star (as it passes along our line of sight). Additionally, if some clumps of matter from this collision were collided into high-eccentricity comet-like orbits, they could explain the flickering from Boyajian et al., but this model doesn’t do a nice job of explaining the long-term dimming. Other researchers are working to develop different models to explain what we see, but they’re still working on these models and haven’t submitted them for publication yet. Broadly speaking, all three effects we observe cannot be explained by any known stellar phenomenon, so it’s almost certainly the result of some material along our line of sight passing between us and the star. We just have to figure out what!”

So the question remains, what accounts for this strange dimming effect around this star? Is there yet some singular stellar phenomena that could account for it all? Or is this just the result of good timing, with astronomers being fortunate enough to see  a combination of a things at work in the same period? Hard to say, and the only way we will know for sure is to keep our eye on this strangely dimming star.

And in the meantime, will the alien enthusiasts not see this as a possible resolution to the Fermi Paradox? Most likely!

Further Reading: arXiv

Student Discovers Four New Planets

The four new, but as yet unconfirmed, exoplanets. Image: University of British Columbia

A student at the University of British Columbia (UBC), Canada, has discovered four new exoplanets hidden in data from the Kepler spacecraft.

Michelle Kunimoto recently graduated from UBC with a Bachelor’s degree in physics and astronomy. As part of her coursework, she spent a few months looking closely at Kepler data, trying to find planets that others had overlooked.

In the end, she discovered four planets, (or planet candidates until they are independently confirmed.) The first planet is the size of Mercury, two are roughly Earth-sized, and one is slightly larger than Neptune. According to Kunimoto, the largest of the four, called KOI (Kepler Object of Interest) 408.05, is the most interesting. That one is 3,200 light years away from Earth and occupies the habitable zone of its star.

“Like our own Neptune, it’s unlikely to have a rocky surface or oceans,” said Kunimoto, who graduates today from UBC. “The exciting part is that like the large planets in our solar system, it could have large moons and these moons could have liquid water oceans.”

Her astronomy professor, Jaymie Matthews, shares her enthusiasm. “Pandora in the movie Avatar was not a planet, but a moon of a giant planet,” he said. And we all know what lived there.

On its initial mission, Kepler looked at 150,000 stars in the Milky Way. Kepler looks for dips in the brightness of these stars, which can be caused by planets passing between us and the star. These dips are called light curves, and they can tell us quite a bit about an exoplanet.

“A star is just a pinpoint of light so I’m looking for subtle dips in a star’s brightness every time a planet passes in front of it,” said Kunimoto. “These dips are known as transits, and they’re the only way we can know the diameter of a planet outside the solar system.”

Michelle Kunimoto and her prof., Jaymie Matthews, at the University of British Columbia in Vancouver, Canada. Image: Martin Dee/UBC
Michelle Kunimoto and her prof., Jaymie Matthews, at the University of British Columbia in Vancouver, Canada. Image: Martin Dee/UBC

One of the limitations of the Kepler mission is that it’s biased against planets that take a long time to orbit their star. That’s because the longer the orbit is, the fewer transits can be witnessed in a given amount of time. The “warm Neptune” KOI 408.05 found by Kunimoto takes 637 days to orbit its sun.

This long orbit explains why the planet was not found initially, and also why Kunimoto is receiving recognition for her discovery. It took a substantial commitment and effort to uncover it. Kepler has discovered almost 5,000 planet and planet candidates, and of those, only 20 have longer orbits than KOI 408.05.

Kunimoto and Matthews have submitted the findings to the Astronomical Journal. They may be the first of many submissions for Kunimoto, as she is returning to UBC next year to earn a Master’s Degree in physics and astronomy, when she will hunt for more planets and investigate their habitability.

The fun didn’t end with her exoplanet discovery, however. As a Star Trek fan (who isn’t one?) she was lucky enough to meet William Shatner at an event at the University, and to share her discovery with Captain James Tiberius Kirk.

It makes you wonder what other surprises might lie hidden in the Kepler data, and what else might be uncovered. Might a life-bearing planet or moon, maybe the only one, be found in Kepler’s data at some future time?

You can read Kunimoto’s paper here.

2007 OR10 Needs A Name. We Suggest Dwarfplanet McDwarfplanetyface

Results of a study combining Kepler observations with Herschel data show that 2007 OR10 is the largest unnamed dwarf planet in our Solar System, and the third largest overall. Illustration: Konkoly Observatory/András Pál, Hungarian Astronomical Association/Iván Éder, NASA/JHUAPL/SwRI

Depending on shifting definitions of what exactly is or isn’t a dwarf planet, our Solar System has about half a dozen dwarf planets. They are: Pluto, Eris, Haumea, Makemake, Ceres, and 2007 OR10.

Even though 2007 OR10’s name makes it stand out from the rest, dwarf planets as a group are an odd bunch. They spend their time in the cold, outer reaches of the Solar System, with Ceres being the only exception. Ceres resides in the asteroid belt between Mars and Jupiter.

Their distance from Earth makes them difficult targets for observation, even with the largest telescopes we have. Even the keen eye of the Hubble Telescope, orbiting above Earth’s view-inhibiting atmosphere, struggles to get a good look at the dwarf planets. But astronomers using the Kepler spacecraft discovered that its extreme light sensitivity have made it a useful tool to study the dwarves.

In a paper published in The Astronomical Journal, a team led by Andras Pal, at Konkoly Observatory in Budapest, Hungary, have refined the measurement of 2007 OR10. Using the Kepler’s observational prowess, and combining it with archival data from the Herschel Space Observatory, the team has come up with a much more detailed understanding of 2007 OR10.

Previously, 2007 OR10 was thought to be about 1280 km (795 miles) in diameter. But the problem is the dwarf planet was only a faint, tiny, and distant point of light. Astronomers knew it was there, but didn’t know much else. Objects as far away as 2007 OR10, which is currently twice as far away from the Sun as Pluto is, can either be small, bright objects, or much larger, dimmer objects that reflect less light.

This is where the Kepler came in. It has exquisite sensitivity to tiny changes in light. Its whole mission is built around that sensitivity. It’s what has made Kepler such an effective tool for identifying exo-planets. Pointing it towards a tiny target like 2007 OR10, and monitoring the reflected light as the object rotates, is a logical use for Kepler.

Even so, Kepler alone wasn’t able to give the team a thorough understanding of the dwarf planet with the clumsy name.

Enter the Herschel Space Observatory, a powerful infrared space telescope. Herschel and its 3.5 metre (11.5 ft.) mirror were in operation at LaGrange 2 from 2009 to 2013. Herschel discovered many things in its mission-span, including solid evidence for comets being the source of water for planets, including Earth.

But the Herschel Observatory also bequeathed an enormous archive of data to astronomers and other space scientists. And that data was crucial to the new measurement of 2007 OR10.

Combining data and observations from multiple sources is not uncommon, and is often the only way to learn much about distant, tiny objects. In this case, the two telescopes were together able to determine the amount of sunlight reflected by the dwarf planet, using Kepler’s light sensitivity, and then measure the amount of that light later radiated back as heat, using Herschel’s infrared capabilities.

Combining those datasets gave a much clearer idea of the size, and reflectivity, of 2007 OR10. In this case, the team behind the new paper was able to determine that 2007 OR10 was significantly larger than previously thought. It’s measured size is now 1535 km (955 mi) in diameter. This is 255 km (160 mi) larger than previously measured.

It also tells us that the dwarf planet’s gravity is stronger, and the surface darker, than previously measured. This further cements the oddball status of 2007 OR10, since other dwarf planets are much brighter. Other observations of the planet have shown that is has a reddish color, which could be the result of methane ice on the surface.

Lead researcher Andras Pal said, “Our revised larger size for 2007 OR10 makes it increasingly likely the planet is covered in volatile ices of methane, carbon monoxide and nitrogen, which would be easily lost to space by a smaller object. It’s thrilling to tease out details like this about a distant, new world — especially since it has such an exceptionally dark and reddish surface for its size.”

Now that more is known about 2007 OR10, perhaps its time it was given a better name, something that’s easier to remember and that helps it fit in with its peer planets Pluto, Ceres, Eris, Haumea, and Makemake. According to convention, the honor of naming it goes to the planet’s discoverers, Meg Schwamb, Mike Brown and David Rabinowitz. They discovered it in 2007 during a search for distant bodies in the Solar System.

According to Schwamb, “The names of Pluto-sized bodies each tell a story about the characteristics of their respective objects. In the past, we haven’t known enough about 2007 OR10 to give it a name that would do it justice. I think we’re coming to a point where we can give 2007 OR10 its rightful name.”

The Universe is vast, and we need some numbered, structured way to name everything. And these names have to mean something scientifically. That’s why objects end up with names like 2007 OR10, or SDSS J0100+2802, the name given to a distant, ancient quasar. But objects closer to home, and certainly everything in our Solar System, deserves a more memory-friendly name.

So what’s it going to be? If you think you have a great name for the oddball dwarf named 2007 OR10, let us hear it in a tweet, or in the comments section.

Spinning Worlds: Orrery of Kepler’s Exoplanets, Part IV

The past few years, Daniel Fabrycky from the Kepler spacecraft science team has put together some terrific orrery-type visualization of all the multiple-planet systems discovered by the Kepler spacecraft. An orrery, as you probably know, is a a mechanical model of a solar system, and the metal or plastic ones available these days usually show the relative positions and motions of our own Sun, Earth, Moon and other planets.

However, the Kepler version of the orreries that have been created are video visualizations of the planetary systems discovered by the Kepler mission that have more than one transiting object. This latest version was created by astronomy graduate student Ethan Kruse and it shows all of the Kepler multi-planet systems (1705 planets in 685 systems as of November 24, 2015) on the same scale as our own Solar System (the dashed lines on the right side of the video).

In the description of the video Kruse said the size of the orbits are all to scale, but the size of the planets are not. “For example, Jupiter is actually 11 times larger than Earth, but that scale makes Earth-size planets almost invisible (or Jupiters annoyingly large),” he explained. “The orbits are all synchronized such that Kepler observed a planet transit every time it hits an angle of 0 degrees (the 3 o’clock position on a clock).”

Additionally, planet colors are based on their approximate equilibrium temperatures, as shown in the legend.

If you think these orreries are pretty great, you can now try your hand at making your own. Kruse said he likes open source and that any software he writes will be available on GitHub. You can get the source code here.

Enjoy!