The James Webb Space Telescope inside a cleanroom at NASA’s Johnson Space Center in Houston. Credit: NASA/JSC
When the James Webb Space Telescope finally takes to space, it will study some of the most distant objects in the Universe, effectively looking back in time to see the earliest light of the cosmos. It will also study extra-solar planets around nearby stars and even bodies within the Solar System. In this respect, the JWST is the natural successor to Hubble and other pioneering space telescopes.
It is therefore understandable why the world is so eager for the JWST to be launched into space (which is now scheduled to take place in 2019). And recently, the telescope passed another major milestone along the road towards deployment. After spending three months in a chamber designed to simulate the temperatures and vacuum conditions of space, the JWST emerged and was given a clean bill of health.
The tests took place inside Chamber A, a thermal vacuum testing facility located at the Johnson Space Center in Houston, Texas. This chamber was built back in 1965 as part of NASA’s race to the Moon, where it conducted tests to ensure that the Apollo command and service modules were space-worthy. Beginning in mid-July, the telescope was put into the chamber and subjected to temperatures ranging from 20 to 40 K (-253 to -233 °C; 423 to 387 °F).
NASA’s James Webb Space Telescope sits in Chamber A at NASA’s Johnson Space Center in Houston awaiting the colossal door to close in July 2017 for cryogenic testing. Credits: NASA/Chris Gunn
Once the temperature and vacuum conditions were just right, a team of NASA engineers began testing the alignment of the JWST’s 18 primary mirror segments to make sure they would act as a single, 6.5-meter telescope. As Bill Ochs – the James Webb telescope project manager at NASA’s Goddard Space Flight Center – indicated to ArsTechnica, this latest test has shown that the telescope is indeed space-worthy.
“We now have verified that NASA and its partners have an outstanding telescope and set of science instruments,” he said. “We are marching toward launch.”
The team of engineers also tested the JWST’s guidance and optical systems by simulating the light of a distant star. Not only was the telescope able to detect the light, its optical systems were able to process it. The telescope was also able to track the simulated star’s movement, which demonstrated that the JWST will be able to acquire and hold research targets once it is in space.
Many tests are still needed before the JWST can take to space next year. These will be conducted at Northrop Grumman’s company headquarters in Los Angeles, where the telescope will be transported after leaving the Johnson Space Center in late January or early February. Once there, the optical instrument will mated to the spacecraft and sunshield to complete the construction of the telescope.
The sunshield test unit on NASA’s James Webb Space Telescope is unfurled for the first time. Credit: NASA
These tests are necessary since NASA will be hard-pressed to service the telescope once it is in space. This is due to the fact that it will be operating at the Earth-Sun L2 Lagrange Point (which will place farther away from Earth than the Moon) for a minimum of five years. At this distance, any servicing missions will be incredibly difficult, time-consuming and expensive to mount.
However, once the JWST has passed its entire battery of tests and NASA is satisfied it is ready to take to space, it will be shipped off to the Guiana Space Center in Kourou, French Guiana. Once there, it will launch aboard a European Space Agency (ESA) Ariane V booster. Originally, this was scheduled to take place in October of 2017, but is now expected to take place no earlier than Spring of 2018.
When the James Webb Space Telescope is operational, it is expected to reveal some truly amazing things about our Universe. In addition to looking farther into space than any previous telescope (and further back in time), its other research goals include studying nearby exoplanets in unprecedented detail, circumstellar debris disks, supermassive black holes at the centers of galaxies, and even searching for life in the Solar System by examining Jupiter’s moons.
For this reason, NASA can be forgiven for pushing the launch back to make sure everything is in working order. But of course, we can be forgiven for wanting to see it launched as soon as possible! There are mysteries out there that are just waiting to be revealed, and some amazing scientific finds that need to be followed up on.
In the meantime, be sure to check out this video about the JWST, courtesy of NASA:
Artist's impression of a hypothetical planet orbiting the star Alpha Centauri B, a member of the triple star system that is the closest to Earth. Credit: ESO
At a distance of 4.37 light-years from Earth, Alpha Centauri is the nearest star system to our own. For generations, scientists and speculative thinkers have pondered whether it might have a planetary system like our own Sun, and whether or not life may also exist there. Unfortunately, recent efforts to locate extra-solar planets in this star system have failed, with potential detections later shown to be the result of artifacts in the data.
In response to these failed efforts, several more ambitious projects are being developed to find exoplanets around Alpha Centauri. These include direct-imaging space telescopes like Project Blue and the interstellar mission known as Breakthrough Starshot. But according to a new study led by researchers from Yale University, existing data can be used to determine the probability of planets in this system (and even which kind).
The study which detailed their findings recently appeared in The Astronomical Journal under the title “Planet Detectability in the Alpha Centauri System“. The study was led by Lily Zhao, a graduate student from Yale University and a fellow with the National Science Foundation (NSF), and was co-authored by Debora Fischer, John Brewer and Matt Giguere of Yale and Bárbara Rojas-Ayala of the Universidad Andrés Bello in Chile.
Artist’s impression of what the surface might look like on a planet orbiting Alpha Centauri system. Credit: Michael S. Helfenbein
For the sake of their study, Zhao and her team considered why efforts to locate planets within the the closest star system to our own have so far failed. This is surprising when one considers how, statistically speaking, Alpha Centauri is very likely to have a system if its own. As Prof. Fischer indicated in a recent Yale News press release:
“The universe has told us the most common types of planets are small planets, and our study shows these are exactly the ones that are most likely to be orbiting Alpha Centauri A and B… Because Alpha Centauri is so close, it is our first stop outside our solar system. There’s almost certain to be small, rocky planets around Alpha Centauri A and B.”
In addition to being a professor of astronomy at Yale University, Debora Fischer is also one of the leaders of the Yale Exoplanets Group. As an expert in her field, Fischer has devoted decades of her life to researching exoplanets and searching for Earth analogues beyond our Solar System. With partial funding provided by NASA and the National Science Foundation, the team relied on existing data collected by some of the latest exoplanet-hunting instruments.
Artist’s impression of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri. The double star Alpha Centauri AB is visible to the upper right of Proxima itself. Credit: ESO
Using ten years of data collected by these instruments, Zhao and her colleagues then set up a grid system for the Alpha Centauri system. Rather than looking for signs of planets that did exist, they used the data to rule out what types of planets could not exist there. As Zhao told Universe Today via email:
“This study was special in that it used existing data of the Alpha Centauri system not to find planets, but to characterize what planets could not exist. By doing so, it returned more information about the system as a whole and provides guidance for future observations of this uniquely charismatic system.
In addition, the team analyzed the chemical composition of the stars in the Alpha Centauri system to learn more about the kinds of material that would be available to form planets. Based on the different values obtained by observations campaigns conducted by different telescopes on Alpha Centauri’s three stars (Alpha, Beta and Proxima), they were able to place constraints on what kinds of planets could exist there.
“We found that existing data rules out planets in the habitable zone above 53 Earth masses for alpha Centauri A, 8.4 Earth masses for Alpha Centauri B, and 0.47 Earth masses for Proxima Centauri,” said Zhao. “As for the chemical compositions, we found that the ratios of Carbon/Oxygen and Magnesium/Silicon for Alpha Centauri A and B are quite similar to that of the Sun.”
Artist’s impression of how the surface of a planet orbiting a red dwarf star may appear. Credit: M. Weiss/CfA
Basically, the results of their study effectively ruled out the possibility of any Jupiter-sized gas giants in the Alpha Centauri system. For Alpha Centauri A, they further found that planets that were less than 50 Earth masses could exist, while Alpha Centauri B might have planets smaller than 8 Earth masses. For Proxima Centauri, which we know to have at least one Earth-like planet, they determined that there might more that are less than half of Earth’s mass.
In addition to offering hope for exoplanet-hunters, this study carries with it some rather interesting implications for planetary habitability. Basically, the presence of rocky planets in the system is encouraging; but with no gas giants, a key ingredient in ensuring that planets remain habitable could be missing.
“[N]ot only could there still be habitable, Earth-mass planets around our closest stellar neighbors, but there also aren’t any gas giants that could endanger the survival of these potentially habitable, rocky planets,” said Zhao. “Furthermore, if these planets do exist, they are likely to have similar compositions to our very own Earth given the similarity in Alpha Cen A/B and our beloved Sun.”
At present, there are no instruments that have been able to confirm the existence of any exoplanets in Alpha Centauri. But as Zhao indicated, her and her teammates are optimistic that future surveys will have the necessary sensitivity to do it:
“[T]his very month has seen the commissioning of several next-generation instruments promising the precision necessary to discover these possible planets in the near future, and this analysis has shown that it is for sure worth it to keep looking!”
The ESO’s Paranal Observatory, located in the Atacama Desert of Chile. Credit: ESO
“These instruments are promising a precision of down to 10-30 cm/s and should be able to detect many more smaller, and further away planets – such as habitable planets around the Centauri stars,” said Zhao. “The field of view of these two instruments are slightly different (ESPRESSO has the southern hemisphere, where Alpha Centauri is, while EXPRES covers the northern hemisphere, for instance where the Kepler and many of the K2 fields are).”
With new instruments at their disposal, and methods like the one Zhao and her team developed, the closest star system to Earth is sure to become a veritable treasure trove for astronomers and exoplanet-hunters in the coming years. And anything we find there will surely become targets for direct studies by groups like Project Blue and Breakthrough Starshot. If ET resides next door, we’re sure to hear about it soon!
Artist's conception of a gas giant orbiting close to its star. Credit: NASA/JPL-Caltech/T. Pyle (SSC)
The discovery of extra-solar planets has certainly heated up in the past few years. With the deployment of the Kepler mission in 2009, several thousands of exoplanet candidates have been discovered and over 2,500 have been confirmed. In many cases, these planets have been gas giants orbiting close to their respective stars (aka. “Hot Jupiters”), which has confounded some commonly-held notions of how and where planets form.
Beyond these massive planets, astronomers also discovered a wide range of planets that range from massive terrestrial planets (“Super-Earths) to Neptune-sized giants. In a recent study, an international team astronomers discovered three new exoplanets orbiting three different stars. These planets are an interesting batch of finds, consisting of two “Hot Saturns” and one Super-Neptune.
From the SuperWASP survey data, Dr. Demangeon and her colleagues were able to detect three transit signals coming from three distant stars – WASP-151, WASP-153 and WASP-156. This was then followed by spectroscopic observations performed using the Haute-Provence Observatory in France and the La Silla Observatory in Chile, which allowed the team to confirm the nature of these planets.
From this, they determined that WASP-151b and WASP-153b are two “hot Saturns”, meaning they are low-density gas giants with close orbits. They orbit their respective suns, which are both early G-type stars (aka. yellow dwarfs, like our Sun), with an orbital period of 4.53 and 3.33 days. WASP-156b, meanwhile, is a Super-Neptune that orbits a K-type (orange dwarf) star. As they indicated in their study:
“WASP-151b and WASP-153b are relatively similar. Their masses of 0.31 and 0.39 M Jup and semi-major axes of 0.056 AU and 0.048 AU respectively indicate two Saturn-size objects around early G type stars of V magnitude ~ 12.8. WASP-156b’s radius of 0.51R Jup suggests a Super-Neptune and makes it the smallest planet ever detected by WASP. Its mass of 0.128 M Jup is also the 3rd lightest detected by WASP after WASP-139b and WASP-107b. Also interesting is the fact that WASP-156 is a bright (magV = 11.6) K type star.”
Number of exoplanets discovered by the Kepler mission as of May 10th, 2016, based on their classification. Credit: W. Stenzel/NASA Ames
Taken together, these planets represent some major opportunities for exoplanet research. As they indicate, “these three planets also lie close to (WASP-151b and WASP-153b) or below (WASP-156b) the upper boundary of the Neptunian desert.” This refers to the boundary astronomers have observed around stars where shot period Neptune-size planets are very unlikely to be found.
Basically, of all the short period exoplanets (less than 10 days) to be discovered so far, the majority have tended to be in the “Super-Earth” or “Super-Jupiter” category. This deficit of Neptune-like planets has been attributed to different mechanisms when it comes to the formation and evolution for hot Jupiters and short-period super-Earths, as well as it being the result of gas envelop-depletion caused by a star’s ultraviolet radiation.
So far, only nine “Super-Neptunes” have been discovered; so this latest discovery (who’s characteristics are well know) should provide plenty of opportunities for research. Or as Dr. Demangeon and her colleagues explain in the study:
“WASP-156b, being one of the few well characterised Super-Neptunes, will help to constrain the formation of Neptune size planets and the transition between gas and ice giants. The estimates of the age of these three stars confirms the tendency for some stars to have gyrochronological ages significantly lower than their isochronal ages.”
Artist’s impression of two super-Earths in the same system as a Neptune-sized exoplanet in the Kepler-62 system. Credit: David A. Aguilar (CfA)
The team also offered some possible explanations for the existence of a “Neptunian desert” based on their findings. For starters, they proposed that a high-eccentricity migration could be responsible, where Neptune-sized ice giants form in the outer reaches of a star system and migrate inward over time. They also indicate that their discovery offers compelling evidence that ultra-violet radiation and gas envelope-depletion could be a key part of the puzzle.
But of course, Dr. Demangeon and her colleagues indicate that further research will be necessary to confirm their hypothesis, and that further studies are needed to properly constrain the boundaries of the so-called “Neptunian desert”. They also indicate that future missions like NASA’s Transiting Exoplanet Survey Satellite and the ESA’s PLAnetary Transits and Oscillations of stars (PLATO) mission will be vital to these efforts.
“Obviously, a more thorough analysis is necessary to investigate all the possible implications behind this hypothesis,” they conclude. “Such an analysis is out of the scope of this paper but we think that this hypothesis is worth investigating. In this context, a search for long period companions that might have triggered the high eccentricity migration or an independent age estimate through asterosiesmology with TESS or Plato would be particularly interesting.”
The sheer number of exoplanets discoveries made in recent decades has allowed astronomers to test and revise commonly-held theories about how planetary systems form and evolve. These same discoveries have also helped advance our understanding of how our own Solar System came to be. In the end, being able to study a diverse array of planetary systems, which are different stages in their history, is allowing us to create a sort of timeline for cosmic evolution.
An artist’s conception of a view from within the Exocomet system KIC 3542116.. Credit: Danielle Futselaar
In the past thirty years, thousands of extra-solar planets have been discovered beyond our Solar System. For the most part, they have been detected by the KeplerSpace Telescope using a technique called Transit Photometry. For this method, astronomers measure periodic dips in a star’s brightness – which are the result of planets passing in front of them relative to an observer – to confirm the presence of planets.
Thanks to a new research effort conducted by a team of professional and amateur astronomers, something much smaller than planets were recently detected orbiting a distant star. According to a new study published by the research team, six exocomets were observed orbiting around KIC 3542116, a spectral type F2V star located 800 light years from Earth. These comets are the smallest objects to date detecting the Transit Photometry method.
Artist’s impression of an orbiting swarm of dusty comet fragments around Tabby’s Star. Credit: NASA/JPL-Caltech
This is the first time that Transit Photometry has been used to detect object as small as comets. These comets were balls of ice and dust – comparable in size to Halley’s Comet – that were found to be traveling at speeds of about 160,934 km/h (100,000 mph) before they vaporized. The researchers were able to detect them by picking out their tails, the clouds of dust and gas that form when comets get closer to their star and begin to sublimate.
This was no easy task, since the tails managed to obscure only about a tenth of 1% of the star’s light. As Saul Rappaport, who is also the professor emeritus of physics at the Kavli Institute for Astrophysics and Space Research, explained in an MIT press release:
“It’s amazing that something several orders of magnitude smaller than the Earth can be detected just by the fact that it’s emitting a lot of debris. It’s pretty impressive to be able to see something so small, so far away.”
Credit for the original detection goes to Thomas Jacobs, an amateur astronomer who lives in Bellevue, Washington, and is a member of Planet Hunters. This citizen scientist project was first established by Yale University and consists of amateur astronomers who dedicated their time to the search for exoplanets. Members are given access to data from the Kepler Space Telescope in the hopes that they would notice things that computer algorithms might miss.
NASA’s Kepler space telescope was the first agency mission capable of detecting Earth-size planets. Credit: NASA/Wendy Stenzel
Back in January, Jacobs began scanning four years of data obtained during Kepler‘s main mission. During this phase, which lasted from 2009 to 2013, Kepler scanned over 200,000 stars and conducted measurements of their light curves. After five months of sifting through the data (on March 18th), he noticed several curious light patterns amid background noise coming from KIC 3542116. As Jacobs said:
“Looking for objects of interest in the Kepler data requires patience, persistence, and perseverance. For me it is a form of treasure hunting, knowing that there is an interesting event waiting to be discovered. It is all about exploration and being on the hunt where few have traveled before.”
Specifically, Jacobs was searching for signs of single transits, which are not like those that are caused by planets orbiting a star (i.e. periodic). While looking at KIC 3542116, he noticed three single transits, and then alerted Rappaport and Andrew Vanderburg, as astrophysicist at University of Texas and member of the CfA. Jacobs had worked with both men in the past, and wanted their opinion on these findings.
As Rapport recalled, the process of interpreting the data was challenging, but rewarding. Initially, they noted that the lightcurves did not resemble those caused by planetary transits, which are characterized by a sudden and sharp drop in light, followed by a sharp rise. In time, Rapport noted the asymmetry in the three lightcurves resembled those of disintegrated planets, which they had observed before.
Artist’s impression of the Epsilon Eridani system, showing Epsilon Eridani b (a Jupiter-mass planet) and a series of asteroid belts and comets. Credit: NASA/SOFIA/Lynette Cook.
“We sat on this for a month, because we didn’t know what it was — planet transits don’t look like this,” said Rappaport. “Then it occurred to me that, ‘Hey, these look like something we’ve seen before’… We thought, the only kind of body that could do the same thing and not repeat is one that probably gets destroyed in the end. The only thing that fits the bill, and has a small enough mass to get destroyed, is a comet.”
Based on their calculations, which indicated that each comet blocked out about one-tenth of 1% of the star’s light, the research team concluded that the comet likely disintegrated entirely, creating a dust trail that was sufficient to block out light for several months before it disappeared. After conducting additional observations, they also noted three more transits in the same time period that were similar to the ones noticed by Jacobs.
The fact that these six exocomets appear to have transited very close to their star in the past four years raises some interesting questions, and answering them could have drastic implications for extra-solar research. It could also advance our understanding of our own Solar System. As Vanderburg explained:
“Why are there so many comets in the inner parts of these solar systems? Is this an extreme bombardment era in these systems? That was a really important part of our own solar system formation and may have brought water to Earth. Maybe studying exocomets and figuring out why they are found around this type of star… could give us some insight into how bombardment happens in other solar systems.”
This artist’s conception illustrates a storm of comets around a star near our own. Credit: NASA/JPL-Caltech
Between 4.1 and 3.8 billion years ago, the Solar System also experienced a period of intense comet activity known as the Late Heavy Bombardment. During this time, asteroids and comets are believed to have impacted bodies in the inner Solar System on a regular basis. Interestingly, this period of heavy bombardment is believed to be what was responsible for the distribution of water to Earth and the other terrestrial planets.
As noted, KIC 3542116 belongs to the spectral type F2V, a yellow-white class of star that is typically 1 to 1.4 times as massive as our Sun and quite bright. Since it is comparable in size and mass to our Sun, it is possible that the bombardment period it is experiencing is similar to what the Solar System went through. Watching it unfold could therefore tell us much about how similar activity influenced the evolution of our Solar System billions of years ago.
In addition to the study’s significance to the study of astrophysics and astronomy, it also demonstrates the important role citizen scientists play today. Were it not for the tireless work performed by Jacobs, who sifts through Kepler data between working his day job and on the weekends, this discovery would not have been possible.
“I could name 10 types of things these people have found in the Kepler data that algorithms could not find, because of the pattern-recognition capability in the human eye,” said Rappaport. “You could now write a computer algorithm to find this kind of comet shape. But they were missed in earlier searches. They were deep enough but didn’t have the right shape that was programmed into algorithms. I think it’s fair to say this would never have been found by any algorithm.”
In the future, the research team expects that the deployment Transiting Exoplanet Survey Satellite (TESS) – which will be led by MIT – will continue to conduct the type of research performed by Kepler.
Artist's concept of the Project Blue space telescope, which the organization hopes to use to spot exoplanets in Alpha Centauri beginning in 2020. Credit: projectblue.org
In the past few decades, thousands of exoplanets have been discovered in neighboring star systems. In fact, as of October 1st, 2017, some 3,671 exoplanets have been confirmed in 2,751 systems, with 616 systems having more than one planet. Unfortunately, the vast majority of these have been detected using indirect means, ranging from Gravitational Microlensing to Transit Photometry and the Radial Velocity Method.
What’s more, we have been unable to study these planets up close because the necessary instruments do not yet exist. Project Blue, a consortium of scientists, universities and institutions, is looking to change that. Recently, they launched a crowdfunding campaign through Indiegogo to finance the development of a space telescope that will start looking for exoplanets in the Alpha Centauri system by 2021.
Artist’s impression of a planet orbiting the star Alpha Centauri B, a member of the triple star system that is the closest to Earth. Credit: ESO
To accomplish their goal of directly studying exoplanets, Project Blue is seeking to leverage recent changes in space exploration, which include improved instruments and methodology, the rate at which exoplanet have been discovered in recent years, and increased collaboration between the private and public sector. As SETI Institute President and CEO Bill Diamond explained in a recent SETI press statement:
“Project Blue builds on recent research in seeking to show that Earth is not alone in the cosmos as a planet capable of supporting life, and wouldn’t it be amazing to see such a planet in our nearest neighboring star system? This is the fundamental reason we search.”
As noted, virtually all exoplanet discoveries that have been made in the past few decades were done using indirect methods – the most popular of which is Transit Photometery. This method is what the Kepler and K2 missions relied on to detect a total of 5,017 exoplanet candidates and confirm the existence of 2,470 exoplanets (30 of which were found to orbit within their star’s habitable zone).
This method consists of astronomers monitoring distant stars for periodic dips in brightness, which are caused by a planet transiting in front of the star. By measuring these dips, scientists are able to determine the size of planets in that system. Another popular technique is the Radial Velocity (or Doppler) Method, which measures changes in a star’s position relative to the observer to determine how massive its system of planets are.
Project Blue’s mission concept, showing the telescope, its launch and deployment. Credit: projectblue.org
These and other methods (alone or in combination) have allowed for the many discoveries that have been made to take place. But so far, no exoplanets have been directly imaged, which is due to the cancelling effect stars have on optical instruments. Basically, astronomers have been unable to spot the light being reflected off of an exoplanet’s atmosphere because the light coming from the star is up to ten billion times brighter.
The challenge has thus become how to go about blocking this light so that the planets themselves can become visible. One proposed solution to this problem is NASA’s Starshade concept, a giant space structure that would be deployed into orbit alongside a space telescope (most likely, the James Webb Space Telescope). Once in orbit, this structure would deploy its flower-shaped foils to block the glare of distant stars, thus allowing the JWST and other instruments to image exoplanets directly.
But since Alpha Centauri is a binary system (or trinary, if you count Proxima Centauri), being able to directly image any planets around them is even more complicated. To address this, Project Blue has developed plans for a telescope that will be able to suppress light from both Alpha Centauri A and B, while simultaneously taking images of any planets that orbit them. It’s specialized starlight suppression system consists of three components.
First, there is the coronagraph, an instrument which will rely on multiple techniques to block starlight. Second, there’s the deformable mirror, low-order wavefront sensors, and software control algorithms that will manipulate incoming light. Last, there is the post-processing method known as Orbital Differntial Imaging (ODI), which will allow the Project Blue scientist to enhance the contrast of the images taken.
Project Blue’s mission timeline, which woudl commence at the end of the decade and run for six years. Credit: projectblue.org
Given its proximity to Earth, the Alpha Centauri system is the natural choice for conducting such a project. Back in 2012, an exoplanet candidate – Alpha Centauri Bb – was announced. However, in 2015, further analysis indicated that the signal detected was an artefact in the data. In March of 2015, a second possible exoplanet (Alpha Centauri Bc) was announced, but its existence has also come to be questioned.
With an instrument capable of directly imaging this system, the existence of any exoplanets could finally be confirmed (or ruled out). As Franck Marchis – the Senior Planetary Astronomer at the SETI Institute and Project Blue Science Operation Lead – said of the Project:
“Project Blue is an ambitious space mission, designed to answer to a fundamental question, but surprisingly the technology to collect an image of a “Pale Blue Dot” around Alpha Centauri stars is there. The technology that we will use to reach to detect a planet 1 to 10 billion times fainter than its star has been tested extensively in lab, and we are now ready to design a space-telescope with this instrument.”
If Project Blue meets its crowdfunding goals, the organization intends to deploy the telescope into Near-Earth Orbit (NEO) by 2021. The telescope will then spend the next two years observing the Alpha Centauri system with its corongraphic camera. All told, between the development of the instrument and the end of its observation campaign, the mission will last six years, a relatively short run for an astronomical mission.
Project Starshot, an initiative sponsored by the Breakthrough Foundation, is intended to be humanity’s first interstellar voyage. Credit: breakthroughinitiatives.org
However, the potential payoff for this mission would be incredibly profound. By directly imaging another planet in the closest star system to our own, Project Blue could gather vital data that would indicate if any planets there are habitable. For years, astronomers have attempted to learn more about the potential habitability of exoplanets by examining the spectral data produced by light passing through their atmospheres.
However, this process has been limited to massive gas giants that orbit close to their parent stars (i.e. “Super-Jupiters”). While various models have been proposed to place constraints on the atmospheres of rocky planets that orbit within a star’s habitable zone, none have been studied directly. Therefore, if it should prove to be successful, Project Blue would allow for some of the greatest scientific finds in history.
What’s more, it would provide information that could a long way towards informing a future mission to Alpha Centauri, such as Breakthrough Starshot. This proposed mission calls for the use of a large laser array to propel a lightsail-driven nanocraft up to relativistic speeds (20% the speed of light). At this rate, the craft would reach Alpha Centauri within 20 years time and be able to transmit data back using a series of tiny cameras, sensors and antennae.
As the name would suggest, Project Blue hopes to capture the first images of a “Pale Blue Dot” that orbits another star. This is a reference to the photograph of Earth that was taken by the Voyager 1 probe on February 19th, 1990, after the probe concluded its primary mission and was getting ready to leave the Solar System. The photos were taken at the request of famed astronomer and science communicator Carl Sagan.
The “Pale Blue Dot” photograph taken by the Voyager 1 probe. Credit: NASA/JPL
When looking at the photographs, Sagan famously said: “Look again at that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives.” Thereafter, the name “Pale Blue Dot” came to be synonymous with Earth and capture the sense of awe and wonder that the Voyage 1 photographs evoked.
More recently, other “Pale Blue Dot” photographs have been snapped by missions like the Cassini orbiter. While photographing Saturn and its system of rings in the summer of 2013, Cassini managed to capture images that showed Earth in the background. Given the distance, Earth once again appeared as a small point of light against the darkness of space.
Beyond relying on crowdfunding and the participation of multiple non-profit organizations, this low-cost mission also seeks to capitalize on a growing trend in space exploration, – which is open participation and collaborations between scientific institutions and citizen scientists. This is one of the primary purposes behind Project Blue, which is to engage the public and educate them about the importance of space exploration.
As Jon Morse, the CEO of the BoldlyGo Institute, explained:
“The future of space exploration holds boundless potential for answering profound questions about our existence and destiny. Space-based science is a cornerstone for investigating such questions. Project Blue seeks to engage a global community in a mission to search for habitable planets and life beyond Earth.”
As of the penning of this article, Project Blue has managed to raise $125,561 USD of their goal of $175,000. For those interesting in backing this project, Project Blue’s Indiegogo campaign will remain open for another 11 days. And be sure to check out their promotional video as well:
Artist's impression of a hypothetical Earth-like moon around a Saturn-like exoplanet. Credit: Wikipedia Commons/
Frizaven
Finding planets beyond our Solar System is already tough, laborious work. But when it comes to confirmed exoplanets, an even more challenging task is determining whether or not these worlds have their own satellites – aka. “exomoons”. Nevertheless, much like the study of exoplanets themselves, the study of exomoons presents some incredible opportunities to learn more about our Universe.
Of all possible candidates, the most recent (and arguably, most likely) one was announced back in July 2017. This moon, known as Kepler-1625 b-i, orbits a gas giant roughly 4,000 light years from Earth. But according to a new study, this exomoon may actually be a Neptune-sized gas giant itself. If true, this will constitute the first instance where a gas giant has been found orbiting another gas giant.
An artist’s conception of a habitable exomoon orbiting a gas giant. Credit: NASA
Within the Solar System, moons tell us much about their host planet’s formation and evolution. In the same way, the study of exomoons is likely to provide insight into extra-solar planetary systems. As Dr. Heller explained to Universe Today via email, these studies could also shed light on whether or not these systems have habitable planets:
“Moons have proven to be extremely helpful to study the formation and evolution of the planets in the solar system. The Earth’s Moon, for example, was key to set the initial astrophysical conditions, such as the total mass of the Earth and the Earth’s primordial spin state, for what has become our habitable environment. As another example, the Galilean moons around Jupiter have been used to study the conditions of the primordial accretion disk around Jupiter from which the planet pulled its mass 4.5 billion years ago. This accretion disk has long gone, but the moons that formed within the disk are still there. And so we can use the moons, in particular their contemporary composition and water contents, to study planet formation in the far past.”
When it comes to the Kepler-1625 star system, previous studies were able to produce estimates of the radii of both Kepler-1625 b and its possible moon, based on three observed transits it made in front of its star. The light curves produced by these three observed transits are what led to the theory that Kepler-1625 had a Neptune-size exomoon orbiting it, and at a distance of about 20 times the planet’s radius.
But as Dr. Heller indicated in his study, radial velocity measurements of the host star (Kepler-1625) were not considered, which would have produced mass estimates for both bodies. To address this, Dr. Heller considered various mass regimes in addition to the planet and moon’s apparent sizes based on their observed signatures. Beyond that, he also attempted to place the planet and moon into the context of moon formation in the Solar System.
Artist’s impression of an exomoon orbiting a gas giant (left) and a Neptune-sized exoplanet (right). Credit: NASA/JPL-Caltech
The first step, accroding to Dr. Heller, was to conduct estimates of the possible mass of the exomoon candidate and its host planet based on the properties that were shown in the transit lightcurves observed by Kepler.
“A dynamical interpretation of the data suggests that the host planet is a roughly Jupiter-sized (“size” in terms of radius) brown dwarf with a mass of almost 18 Jupiter masses,” he said. “The uncertainties, however, are very large mostly due to the noisiness of the Kepler data and due to the low number of transits (three). In fact, the host object could be a Jupiter-like planet or even be a moderate-sized brown dwarf of up to 37 Jupiter masses. The mass of the moon candidate ranges somewhere between a super-Earth of a few Earth masses and Neptune’s mass.”
Next, Dr. Heller compared the relative mass of the exomoon candidate and Kepler-1625 b and compared this value to various planets and moons of the Solar System. This step was necessary because the moons of the Solar System show two distinct populations, based the mass of the planets compared to their moon-to-planet mass ratios. These comparisons indicate that a moon’s mass is closely related to how it formed.
For instance, moons that formed through impacts – such as Earth’s Moon, and Pluto’s moon Charon – are relatively heavy, whereas moons that formed from a planet’s accretion disk are relatively light. While Jupiter’s moon Ganymede is the most massive moon in the Solar System, it is rather diminutive and tiny compared to Jupiter itself – the largest and most massive body in the Solar System.
Artist’s impression of the view from a hypothetical moon around a exoplanet orbiting a triple star system. Credit: NASA
In the end, the results Dr. Heller obtained proved to be rather interesting. Basically, they indicated that Kepler-1625 b-i cannot be definitively placed in either of these families (heavy, impact moons vs. lighter, accretion moons). As Dr. Heller explained:
“[T]]he most reasonable scenarios suggest that the moon candidate is more of the heavy kind, which suggests it should have formed through an impact. However, this exomoon, if real, is most likely gaseous. The solar system moons are all rocky/icy bodies without a significant gas envelope (Titan has a thick atmosphere but its mass is negligible). So how would a gas giant moon have formed through an impact? I don’t know. I don’t know if anybody knows.
“Alternatively, in a third scenario, Kepler-1625 b-i could have formed through capture, but this implies a very unlikely progenitor planetary binary system, from which it was pulled into a bound orbit around Kepler-1625 b, while its former planetary companion was ejected from the system.”
What was equally interesting were the mass estimates for Keple-1625 b, which Dr. Heller averaged to be 19 Jupiter masses, but could be as high as 112 Jupiter Masses. This means that the host planet could be anything from a gas giant that is just slightly larger than Saturn to a Brown Dwarf or even a Very-Low-Mass-Star (VLMS). So rather than a gas giant moon orbiting a gas giant, we could be dealing with a gas giant moon orbiting a small star, which together orbit a larger star!
An artist’s conception of a T-type brown dwarf. Credit: Tyrogthekreeper/Wikimedia Commons.
It’s the stuff science fiction is made of! And while this study cannot provide exact mass constraints on Keplder-1625 b and its possible moon, its significance cannot be denied. Beyond providing astrophysicists with the first possible example of a gas giant moon, this study is of immense significance as far as the study of exoplanet systems is concerned. If and when Kepler-1625 b-i is confirmed, it will tell us much about the conditions under which its host formed.
In the meantime, more observations are needed to confirm or rule out the existence of this moon. Fortunately, these observations will be taking place in the very near future. When Kepler-1625 b makes it next transit – on October 29th, 2017 – the Hubble Space Telescope will be watching! Based on the light curves it observes coming from the star, scientist should be able to get a better idea of whether or not this mysterious moon is real and what it looks like.
“If the moon turns out to be a ghost in the data, then most of this study would not be applicable to the Kepler-1625 system,” said Dr. Heller. “The paper would nevertheless present an example study of how to classify future exomoons and how to put them into the context of the solar system. Alternatively, if Kepler-1625 b-i turns out to be a genuine exomoon, then my study suggests that we have found a new kind of moon that has a very different formation history than the moons we know as of today. Certainly an exquisite riddle for astrophysicists to solve.”
The study of exoplanet systems is like pealing an onion, albeit in a dark room with the lights turned off. With every successive layer scientists peel back, the more mysteries they find. And with the deployment of next-generation telescopes in the near future, we are bound to learn a great deal more!
The outer planets of our Solar System at approximately relative sizes. From left, Jupiter, Saturn, Uranus and Neptune. Credit: Lunar and Planetary Institute
Between the planets of the inner and outer Solar System, there are some stark differences. The planets that resides closer to the Sun are terrestrial (i.e. rocky) in nature, meaning that they are composed of silicate minerals and metals. Beyond the Asteroid Belt, however, the planets are predominantly composed of gases, and are much larger than their terrestrial peers.
This is why astronomers use the term “gas giants” when referring to the planets of the outer Solar System. The more we’ve come to know about these four planets, the more we’ve come to understand that no two gas giants are exactly alike. In addition, ongoing studies of planets beyond our Solar System (aka. “extra-solar planets“) has shown that there are many types of gas giants that do not conform to Solar examples. So what exactly is a “gas giant”?
Definition and Classification:
By definition, a gas giant is a planet that is primarily composed of hydrogen and helium. The name was originally coined in 1952 by James Blish, a science fiction writer who used the term to refer to all giant planets. In truth, the term is something of a misnomer, since these elements largely take a liquid and solid form within a gas giant, as a result of the extreme pressure conditions that exist within the interior.
The four gas giants of the Solar System (from right to left): Jupiter, Saturn, Uranus and Neptune. Credit: NASA/JPL
What’s more, gas giants are also thought to have large concentrations of metal and silicate material in their cores. Nevertheless, the term has remained in popular usage for decades and refers to all planets – be they Solar or extra-solar in nature – that are composed mainly of gases. It is also in keeping with the practice of planetary scientists, who use a shorthand – i.e. “rock”, “gas”, and “ice” – to classify planets based on the most common element within them.
Hence the difference between Jupiter and Saturn on the one and, and Uranus and Neptune on the other. Due to the high concentrations of volatiles (such as water, methane and ammonia) within the latter two – which planetary scientists classify as “ices” – these two giant planets are often called “ice giants”. But since they are composed mainly of hydrogen and helium, they are still considered gas giants alongside Jupiter and Saturn.
Classification:
Today, Gas giants are divided into five classes, based on the classification scheme proposed by David Sudarki (et al.) in a 2000 study. Titled “Albedo and Reflection Spectra of Extrasolar Giant Planets“, Sudarsky and his colleagues designated five different types of gas giant based on their appearances and albedo, and how this is affected by their respective distances from their star.
Class I: Ammonia Clouds – this class applies to gas giants whose appearances are dominated by ammonia clouds, and which are found in the outer regions of a planetary system. In other words, it applies only to planets that are beyond the “Frost Line”, the distance in a solar nebula from the central protostar where volatile compounds – i.e. water, ammonia, methane, carbon dioxide, carbon monoxide – condense into solid ice grains.
These cutaways illustrate interior models of the giant planets. Jupiter is shown with a rocky core overlaid by a deep layer of metallic hydrogen. Credit: NASA/JPL
Class II: Water Clouds – this applies to planets that have average temperatures typically below 250 K (-23 °C; -9 °F), and are therefore too warm to form ammonia clouds. Instead, these gas giants have clouds that are formed from condensed water vapor. Since water is more reflective than ammonia, Class II gas giants have higher albedos.
Class III: Cloudless – this class applies to gas giants that are generally warmer – 350 K (80 °C; 170 °F) to 800 K ( 530 °C; 980 °F) – and do not form cloud cover because they lack the necessary chemicals. These planets have low albedos since they do not reflect as much light into space. These bodies would also appear like clear blue globes because of the way methane in their atmospheres absorbs light (like Uranus and Neptune).
Class IV: Alkali Metals – this class of planets experience temperatures in excess of 900 K (627 °C; 1160 °F), at which point Carbon Monoxide becomes the dominant carbon-carrying molecule in their atmospheres (rather than methane). The abundance of alkali metals also increases substantially, and cloud decks of silicates and metals form deep in their atmospheres. Planets belonging to Class IV and V are referred to as “Hot Jupiters”.
Class V: Silicate Clouds – this applies to the hottest of gas giants, with temperatures above 1400 K (1100 °C; 2100 °F), or cooler planets with lower gravity than Jupiter. For these gas giants, the silicate and iron cloud decks are believed to be high up in the atmosphere. In the case of the former, such gas giants are likely to glow red from thermal radiation and reflected light.
Artist’s concept of “hot Jupiter” exoplanet, a gas giant that orbits very close to its star. Credit: NASA/JPL-Caltech)
Exoplanets:
The study of exoplanets has also revealed a wealth of other types of gas giants that are more massive than the Solar counterparts (aka. Super-Jupiters) as well as many that are comparable in size. Other discoveries have been a fraction of the size of their solar counterparts, while some have been so massive that they are just shy of becoming a star. However, given their distance from Earth, their spectra and albedo have cannot always be accurately measured.
As such, exoplanet-hunters tend to designate extra-solar gas giants based on their apparent sizes and distances from their stars. In the case of the former, they are often referred to as “Super-Jupiters”, Jupiter-sized, and Neptune-sized. To date, these types of exoplanet account for the majority of discoveries made by Kepler and other missions, since their larger sizes and greater distances from their stars makes them the easiest to detect.
In terms of their respective distances from their sun, exoplanet-hunters divide extra-solar gas giants into two categories: “cold gas giants” and “hot Jupiters”. Typically, cold hydrogen-rich gas giants are more massive than Jupiter but less than about 1.6 Jupiter masses, and will only be slightly larger in volume than Jupiter. For masses above this, gravity will cause the planets to shrink.
Exoplanet surveys have also turned up a class of planet known as “gas dwarfs”, which applies to hydrogen planets that are not as large as the gas giants of the Solar System. These stars have been observed to orbit close to their respective stars, causing them to lose atmospheric mass faster than planets that orbit at greater distances.
For gas giants that occupy the mass range between 13 to 75-80 Jupiter masses, the term “brown dwarf” is used. This designation is reserved for the largest of planetary/substellar objects; in other words, objects that are incredibly large, but not quite massive enough to undergo nuclear fusion in their core and become a star. Below this range are sub-brown dwarfs, while anything above are known as the lightest red dwarf (M9 V) stars.
An artist’s conception of a T-type brown dwarf. Credit: Tyrogthekreeper/Wikimedia Commons
Like all things astronomical in nature, gas giants are diverse, complex, and immensely fascinating. Between missions that seek to examine the gas giants of our Solar System directly to increasingly sophisticated surveys of distant planets, our knowledge of these mysterious objects continues to grow. And with that, so is our understanding of how star systems form and evolve.
The new DARKNESS camera developed by an international team of researchers will allow astronomers to directly study nearby exoplanets. Credit: Stanford/SRL
NASA has turned a lot of heads in recent years thanks to its New Worlds Mission concept – aka. Starshade. Consisting of a giant flower-shaped occulter, this proposed spacecraft is intended to be deployed alongside a space telescope (most likely the James Webb Space Telescope). It will then block the glare of distant stars, creating an artificial eclipse to make it easier to detect and study planets orbiting them.
The only problem is, this concept is expected to cost a pretty penny – an estimated $750 million to $3 billion at this point! Hence why Stanford Professor Simone D’Amico (with the help of exoplanet expert Bruce Macintosh) is proposing a scaled down version of the concept to demonstrate its effectiveness. Known as mDot, this occulter will do the same job, but at a fraction of the cost.
The purpose behind an occulter is simple. When hunting for exoplanets, astronomers are forced to rely predominantly on indirected methods – the most common being the Transit Method. This involves monitoring stars for dips in luminosity, which are attributed to planets passing between them and the observer. By measuring the rate and the frequency of these dips, astronomers are able to determine the sizes of exoplanets and their orbital periods.
As Simone D’Amico, whose lab is working on this eclipsing system, explained in a Stanford University press statement:
“With indirect measurements, you can detect objects near a star and figure out their orbit period and distance from the star. This is all important information, but with direct observation you could characterize the chemical composition of the planet and potentially observe signs of biological activity – life.”
However, this method also suffers from a substantial rate of false positives and generally requires that part of the planet’s orbit intersect a line-of-sight between the host star and Earth. Studying the exoplanets themselves is also quite difficult, since the light coming from the star is likely to be several billion times brighter than the light being reflected off the planet.
The ability to study this reflected light is of particular interest, since it would yield valuable data about the exoplanets’ atmospheres. As such, several key technologies are being developed to block out the interfering light of stars. A spacecraft equipped with an occulter is one such technology. Paired with a space telescope, this spacecraft would create an artificial eclipse in front of the star so objects around it (i.e. exoplanets) can be clearly seen.
But in addition to the significant cost of building one, there is also the issue of size and deployment. For such a mission to work, the occulter itself would need to be about the size of a baseball diamond – 27.5 meters (90 feet) in diameter. It would also need to be separated from the telescope by a distance equal to multiple Earth diameters and would have to be deployed beyond Earth’s orbit. All of this adds up to a rather pricey mission!
Artist’s impression of the mDOT system. Much like the moon in a solar eclipse, one spacecraft would block the light from the star, allowing the other to observe objects near that star. Credit: Space Rendezvous Laboratory/Stanford University
As such, D’Amico – an assistant professor and the head of the Space Rendezvous Laboratory (SRL) at Stanford – and and Bruce Macintosh (a Stanford professor of physics) teamed up to create a smaller version called the Miniaturized Distributed Occulter/Telescope (mDOT). The primary purpose of mDOT is to provide a low-cost flight demonstration of the technology, in the hopes of increasing confidence in a full-scale mission.
As Adam Koenig, a graduate student with the SRL, explained:
“So far, there has been no mission flown with the degree of sophistication that would be required for one of these exoplanet imaging observatories. When you’re asking headquarters for a few billion dollars to do something like this, it would be ideal to be able to say that we’ve already flown all of this before. This one is just bigger.”
Consisting of two parts, the mDOT system takes advantage of recent developments in miniaturization and small satellite (smallsat) technology. The first is a 100-kg microsatellite that is equipped with a 3-meter diameter starshade. The second is a 10-kg nanosatellite that carries a telescope measuring 10 cm (3.937 in) in diameter. Both components will be deployed in high Earth orbit with a nominal separation of less than 1,000 kilometers (621 mi).
With the help of colleagues from the SRL, the shape of mDOT’s starshade was reformulated to fit the constraints of a much smaller spacecraft. As Koenig explained, this scaled down and specially-designed starshade will be able to do the same job as the large-scale, flower-shaped version – and on a budget!
Simone D’Amico’s Space Rendezvous Laboratory, pictured inside the room where they test space navigation in highly realistic illumination conditions. Credit: Space Rendezvous Laboratory/Stanford University
“With this special geometric shape, you can get the light diffracting around the starshade to cancel itself out,” he said. “Then, you get a very, very deep shadow right in the center. The shadow is deep enough that the light from the star won’t interfere with observations of a nearby planet.”
However, since the shadow created by mDOT’s starshade is only tens of centimeters in diameter, the nanosatellite will have do some careful maneuvering to stay within it. For this purpose, D’Amico and the SRL also designed an autonomous system for the nanosatellite, which would allow it to conduct formation maneuvers with the starshade, break formation when needed, and rendezvous with it again later.
An unfortunate limitation to the technology is the fact that it won’t be able to resolve Earth-like planets. Especially where M-type (red dwarf) stars are concerned, these planets are likely to orbit too close to their parent stars to be observed clearly. However, it will be able to resolve Jupiter-sized gas giants and help characterize exozodiacal dust concentrations around nearby stars – both of which are priorities for NASA.
In the meantime, D’Amico and his colleagues will be using the Testbed for Rendezvous and Optical Navigation (TRON) to test their mDOT concept. This facility was specially-built by D’Amico to replicate the types of complex and unique illumination conditions that are encountered by sensors in space. In the coming years, he and his team will be working to ensure that the system works before creating an eventual prototype.
Artist’s concept of the prototype starshade, a giant structure designed to block the glare of stars so that future space telescopes can take pictures of planets. Credit: NASA/JPL
As D’Amico said of the work he and his colleagues at the SNL perform:
“I’m enthusiastic about my research program at Stanford because we’re tackling important challenges. I want to help answer fundamental questions and if you look in all current direction of space science and exploration – whether we’re trying to observe exoplanets, learn about the evolution of the universe, assemble structures in space or understand our planet – satellite formation-flying is the key enabler.”
Other projects that D’Amico and the SNL are currently engaged in include developing larger formations of tiny spacecraft (aka. “swarm satellites”). In the past, D’Amico has also collaborated with NASA on such projects as GRACE – a mission that mapped variations in Earth’s gravity field as part of the NASA Earth System Science Pathfinder (ESSP) program – and TanDEM-X, an SEA-sponsored mission which yielded 3D maps of Earth.
These and other projects which seek to leverage miniaturization for the sake of space exploration promise a new era of lower costs and greater accessibility. With applications ranging from swarms of tiny research and communications satellites to nanocraft capable of making the journey to Alpha Centauri at relativistic speeds (Breakthrough Starshot), the future of space looks pretty promising!
Be sure to check out this video of the TRON facility too, courtesy of Standford University:
In a series of papers, Professor Loeb and Michael Hippke indicate that conventional rockets would have a hard time escaping from certain kinds of extra-solar planets. Credit: NASA/Tim Pyle
Decades after Enrico Fermi’s uttered his famous words – “Where is everybody?” – the Paradox that bears his name still haunts us. Despite repeated attempts to locate radio signals coming from space and our ongoing efforts to find visible indications of alien civilizations in distant star systems, the search extra-terrestrial intelligence (SETI) has yet to produce anything substantive.
Artist's impression of rocky exoplanets orbiting Gliese 832, a red dwarf star just 16 light-years from Earth. Credit: ESO/M. Kornmesser/N. Risinger (skysurvey.org).
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!
