Ever since the first exoplanet was confirmed in 1992, astronomers have found thousands of worlds beyond our Solar System. With more and more discoveries happening all the time, the focus of exoplanet research has begun to slowly shift from exoplanet discovery to exoplanet characterization. Essentially, scientists are now looking to determine the composition of exoplanets to determine whether or not they could support life.
The Kepler space telescope has had a relatively brief but distinguished career of service with NASA. Having launched in 2009, the space telescope has spent the past nine years observing distant stars for signs of planetary transits (i.e. the Transit Method). In that time, it has been responsible for the detection of 2,650 confirmed exoplanets, which constitutes the majority of the more than 38oo planets discovered so far.
Earlier this week, the Kepler team was notified that the space telescope’s fuel tank is running very low. NASA responded by placing the spacecraft in hibernation in preparation for a download of its scientific data, which it collected during its latest observation campaign. Once the data is downloaded, the team expects to start its last observation campaign using whatever fuel it has left.
Since 2013, Kepler has been conducting its “Second Light” (aka. K2) campaign, where the telescope has continued conducting observations despite the loss of two of its reaction wheels. Since May 12th, 2018, Kepler has been on its 18th observation campaign, which has consisted of it studying a patch of sky in the vicinity of the Cancer constellation – which it previously studied in 2015.
In order to send the data back home, the spacecraft will point is large antenna back towards Earth and transmit it via the Deep Space Network. However, the DSN is responsible for transmitting data from multiple missions and time needs to be allotted in advance. Kepler is scheduled to send data from its 18th campaign back in August, and will remain in a stable orbit and safe mode in order to conserve fuel until then.
On August 2nd, the Kepler team will command the spacecraft to awaken and will maneuver the craft to the correct orientation to transmit the data. If all goes well, they will begin Kepler’s 19th observation campaign on August 6th with what fuel the spacecraft still has. At present, NASA expects that the spacecraft will run out of fuel in the next few months.
However, even after the Kepler mission ends, scientists and engineers will continue to mine the data that has already been sent back for discoveries. According to a recent study by an international team of scientists, 24 new exoplanets were discovered using data from the 10th observation campaign, which has brought the total number of Kepler discoveries to 2,650 confirmed exoplanets.
In the coming years, many more exoplanet discoveries are anticipated as the next-generation of space telescopes begin collecting their first light or are deployed to space. These include the Transiting Exoplanet Survey Satellite (TESS), which launched this past April, and the James Webb Space Telescope (JWST) – which is currently scheduled to launch sometime in 2021.
However, it will be many years before any mission can rival the accomplishments and contributions made by Kepler! Long after she is retired, her legacy will live on in the form of her discoveries.
Further Reading: NASA
When it is deployed to space, the James Webb Space Telescope (JWST) will be the most powerful and advanced telescope ever deployed. As the spiritual and scientific successor to the Hubble, Spitzer, and Kepler Space Telescopes, this space observatory will use its advanced suite of infrared instruments to look back at the early Universe, study the Solar System, and help characterize extra-solar planets.
Unfortunately, after many delays, there’s some good news and bad news about this mission. The good news is that recently, the Independent Review Board (IRB) established by NASA to assess the progress on the JWST unanimously decided that work on the space telescope should continue. The bad news is that NASA has decided to push the launch date back again – this time to March 30th, 2021.
As part of their assessment, the IRB was established in April of 2018 to address a range of factors influencing Webb’s schedule and performance. These included the technical challenges and tasks that need to be tackled by its primary contractor (Northrop Grumman) before the mission can launch. A summary of the report’s recommendations, and NASA’s response, can be read here.
In the report, the IRB identified technical issues, which including human errors, that they claim have greatly impacted the development schedule. As they stated in their Overview:
“The observation that there are no small JWST integration and test problems was not initially recognized by the Webb IRB, and this also may be true of others involved with JWST. It is a most important observation that will be apparent in subsequent Findings and Recommendations. It is caused by the complexity and highly integrated nature of the observatory. Specifically, it implies, as an example, that a very small human error or test anomaly can impact the schedule by months and the cost by tens of millions of dollars.”
The anomaly mentioned in the report refers to the “anomalous readings” that were detected from the telescope during vibration testing back in December 2016. NASA responded to this by giving the project up to 4 months of schedule reserve by extending the launch window. However, in 2017, NASA delayed the launch window again by 5 months, from October 2018 to a between March and June 2019.
This delay was requested by the project team, who indicated that they needed to address lessons learned from the initial folding and deployment of the observatory’s sun shield. In February of 2018, the Government Accountability Office (GAO) issued a report that expressed concerns over further delays and cost overruns. Shortly thereafter, the JWST’s Standing Review Board (SRB) made an independent assessment of the remaining tasks.
In May of 2018, NASA issued a statement indicating that they now estimated that the launch window would be some time in May 2020. However, they chose to await the findings of the IRB and consider the data from the JWST’s Standing Review Board before making the final determination. The new launch date was set to accommodate environmental testing and work performances challenges on the sunshield and propulsion system.
According to the IRB report, this latest delay will also result in a budget overrun. “As a result of the delay, Webb’s total lifecycle cost to support the March 2021 launch date is estimated at $9.66 billion,” they concluded. “The development cost estimate to support the new launch date is $8.8B (up from the $8B development cost estimate established in 2011).”
As Jim Bridenstine, the NASA Administrator, indicated in a message to the NASA workforce on Wednesday about the report:
“Webb is vital to the next generation of research beyond NASA’s Hubble Space Telescope. It’s going to do amazing things – things we’ve never been able to do before – as we peer into other galaxies and see light from the very dawn of time. Despite major challenges, the board and NASA unanimously agree that Webb will achieve mission success with the implementation of the board’s recommendations, many of which already are underway.”
In the end, the IRB, SRB and NASA are all in total agreement that the James Webb Space Telescope is a crucial mission that must be seen through. In addition to shedding light on a number of mysteries of the Universe – ranging from the earliest stars and galaxies in the Universe to exoplanet habitability – the JWST will also complement and enhance the discoveries made by other missions.
These include not only Hubble and Spitzer, but also missions like the Transiting Exoplanet Survey Satellite (TESS), which launched this past April. Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate, also issued a statement on the recent report:
“The more we learn more about our universe, the more we realize that Webb is critical to answering questions we didn’t even know how to ask when the spacecraft was first designed. Webb is poised to answer those questions, and is worth the wait. The valuable recommendations of the IRB support our efforts towards mission success; we expect spectacular scientific advances from NASA’s highest science priority.”
The JWST will also be the first telescope of its kind, being larger and more complex than any previous space telescope – so challenges were anticipated from its very inception. In addition, the final phase consists of some of the most challenging work, where the 6.5-meter telescope and science payload element are being joined with the spacecraft element to complete the observatory.
The science team also needs to ensure that the observatory can be folded up to fit inside the Ariane 5 rocket that will launch it into space. They also need to ensure that it will unfold again once it reaches space, deploy its sunshield, mirrors and primary mirror. Beyond that, there are also the technical challenges of building a complex observatory that was created here on Earth, but designed to operate in space.
As a collaborative project between NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA), the JWST is also representative of the new era of international cooperation. As such, no one wishes to see the mission abandoned so close to completion. In the meantime, any delays that allow for extra testing will only ensure success in the long run.
Good luck JWST, we look forward to hearing about your first discoveries!
Further Reading: NASA
The Transiting Exoplanet Survey Satellite (TESS), NASA’s latest exoplanet-hunting space telescope, was launched into space on Wednesday, April 18th, 2018. As the name suggests, this telescope will use the Transit Method to detect terrestrial-mass planets (i.e. rocky) orbiting distant stars. Alongside other next-generation telescopes like the James Webb Space Telescope (JWST), TESS will effectively pick up where telescopes like Hubble and Kepler left off.
But just how many planets is TESS expected to find? That was the subject of a new study by a team researchers who attempted to estimate just how many planets TESS is likely to discover, as well as the physical properties of these planets and the stars that they orbit. Altogether, they estimate TESS will find thousands of planets orbiting a variety of stars during its two-year primary mission.
The study, titled “A Revised Exoplanet Yield from the Transiting Exoplanet Survey Satellite (TESS)“, recently appeared online. The study was led by Thomas Barclay, an associate research scientist at the NASA Goddard Space Flight Center and the University of Maryland, and included Joshua Pepper (an astrophysicist at Lehigh University) and Elisa Quintana (a research scientist with the SETI Institute and NASA Ames Research Center).
As Thomas Barclay told Universe Today via email:
“TESS builds off the legacy of Kepler. Kepler was primarily a statistical mission and taught us that planets are everywhere. However, it wasn’t optimized for finding excellent individual planets for further study. Now that we know planets are common, we can launch something like TESS to search for the planets that we will undertake intensive studies of using ground and space-based telescopes. Planets that TESS will find will on average be 10x closer and 100x brighter.”
For the sake of their study, the team created a three-step model that took into account the stars TESS will observe, the number of planets each one is likely to have, and the likelihood of TESS spotting them. These included the kinds of planets that would be orbiting around dwarf stars ranging from A-type to K-type (like our Sun), and lower-mass M-type (red dwarf) stars.
“To estimate how many planets TESS will find we took stars that will be observed by TESS and simulated a population of planets orbiting them,” said Barclay. “The exoplanet population stats all come from studies that used Kepler data. Then, using models of TESS performance, we estimated how many of those planets would be detected by TESS. This is where we get our yield numbers from.”
The first step was straightforward, thanks to the availability of the Candidate Target List (CTL) – a prioritized list of target stars that the TESS Target Selection Working Group determined were the most suitable stars for detecting small planets. They then ranked the 3.8 million stars that are included in the latest version based on their brightness and radius and determined which of these TESS is likely to observe.
The second step consisted of assigning planets to each star based on a Poisson distribution, a statistical technique where a given number is assigned to each star (in this case, 0 or more). Each planet was then assigned six physical properties drawn at random, including an orbital period, a radius, an eccentricity, a periastron angle, an inclination to our line of sight, and a mid-time of first transit.
Last, they attempted to estimate how many of these planets would generate a detectable transit signal. As noted, TESS will rely on the Transit Method, where periodic dips in a star’s brightness are used to determine the presence of one or more orbiting planets, as well as place constraints on their sizes and orbital periods. For this, they considered the flux contamination of nearby stars, the number of transits, and the transit duration.
Ultimately, they determined with 90% confidence that TESS is likely to detect 4430–4660 new exoplanets during its two years mission:
“The results is that we predict that TESS will find more than 4000 planets, with hundreds smaller than twice the size of Earth. The primary goal of TESS is to find planets that are bright enough for ground-based telescope to measure their mass. We estimate that TESS could lead to triple the number of planets smaller than 4 Earth-radii with mass measurements.”
As of April 1st, 2018, a total 3,758 exoplanets have been confirmed in 2,808 systems, with 627 systems having more than one planet. In other words, Barclay and his team estimate that the TESS mission will effectively double the number of confirmed exoplanets and triple the number of Earth-sized and Super-Earth’s during its primary mission.
This will begin after a series of orbital maneuvers and engineering tests, which are expected to last for about two months. With the exoplanet catalog thus expanded, we can expect that there will be many more “Earth-like” candidates available for study. And while we still will not be able to determine if any of them have life, we may perhaps find some that show signs of a viable atmosphere and water on the surfaces.
The hunt for life beyond Earth will continue for many years to come! And in the meantime, be sure to enjoy this video about the TESS mission, courtesy of NASA:
In the course of searching for planets beyond our Solar System – aka. extra-solar planets – some truly interesting cases have been discovered. In addition to planets that are several times the size of the Solar System’s largest planet (Super-Jupiters), astronomers have also found a plethora of terrestrial (i.e rocky) planets that are several times the size of Earth (Super-Earths).
This is certainly true of K2-229b, a rocky planet that was recently discovered by an international team of astronomers. Located 339 light years away, this hot, metallic planet is an exercise in extremes. Not only is it 20% larger than Earth, it is 2.6 times Earth mass and has a composition similar to Mercury. On top of that, its orbits its star so closely that it is several times hotter than Mercury.
The study which details their discovery recently appeared in the journal Nature under the title “An Earth-sized exoplanet with a Mercury-like composition“. The study was led by Alexandre Santerne, a researcher from the Laboratoire d’Astrophysique de Marseille (LAM) at the Aix-Marseille Université, and included members from the the European Southern Observatory (ESO), the University of Warwick, the Universidade do Porto, and multiple universities and research institutions.
Using data from the Kepler space telescopes K2 mission, the team was able to identify K2-229b, a Super-Earth that orbits a medium-sized K dwarf (orange dwarf) star in the Virgo Constellation. Using the Radial Velocity Method – aka. Doppler Spectroscopy – the team was able to determine the planet’s size and mass, which indicated that it is similar in composition to Mercury – i.e. metallic and rocky.
They were also able to determine that it orbits its star at a distance of 0.012 AU with an orbital period of just 14 days. At this distance, K2-229b is roughly one one-hundredth as far from its star as the Earth is from the Sun and experiences surface temperature that are several times higher than those on Mercury – reaching a day side temperature 2000 °C (3632 °F), or hot enough to melt iron and silicon.
As Dr. David Armstrong, a researcher from the University of Warwick and a co-author on the study, explained:
“Mercury stands out from the other Solar System terrestrial planets, showing a very high fraction of iron and implying it formed in a different way. We were surprised to see an exoplanet with the same high density, showing that Mercury-like planets are perhaps not as rare as we thought. Interestingly K2-229b is also the innermost planet in a system of at least 3 planets, though all three orbit much closer to their star than Mercury. More discoveries like this will help us shed light on the formation of these unusual planets, as well as Mercury itself.”
Given its dense, metallic nature, it is something of a mystery of how this planet formed. One theory is that the planet’s atmosphere could have been eroded by intense stellar wind and flares, given that the planet is so close to its star. Another possibility is that it was formed from a huge impact between two giant bodies billions of years ago – similar to the theory of how the Moon formed after Earth collided with a Mars-sized body (named Theia).
As with many recent discoveries, this latest exoplanet is giving astronomers the opportunity to see just what is possible. By studying how them, we are able to learn more about how the Solar System formed and evolved. Given the similarities between K2-229b and Mercury, the study of this exoplanet could teach us much about how Mercury became a dense, metallic planet that orbits closely to our Sun.
Further Reading: Warwick
Once it deploys, the James Webb Space Telescope (JWST) will be the most powerful and technically complex space telescope ever deployed. Using its powerful suite of infrared-optimized instruments, this telescope will be able to study the earliest stars and galaxies in the Universe, extra-solar planets around nearby stars, and the planets, moons and asteroids of our Solar System.
Unfortunately, due to its complexity and the need for more testing, the launch of the JWST has been subject to multiple delays. And as of this morning, NASA announced that the launch JWST has been delayed yet again. According to a statement issued by the agency, the launch window for the JWST is now targeted for sometime around May 2020.
The decision came after an independent assessment by the project’s Standing Review Board (SRB) of the remaining tasks, all of which are part of the final stage of integration and testing before the JWST launches. These tasks consist of integrating the combined optics and science instruments onto the spacecraft element, then testing them to ensure that they will deploy properly and work once they are in space.
This assessment came on the heels of a report issued by the Government Accountability Office (GAO) in February that expressed concerns over further delays and cost overruns. These concerns were based on the fact that it is typically in the final phase when problems are found and schedules revised, and that only 1.5 months of schedule reserved remained (at the time) until the end of the telescope’s launch window – which was scheduled for 2019.
But as acting NASA Administrator Robert Lightfoot stressed, the JWST is still a go:
“Webb is the highest priority project for the agency’s Science Mission Directorate, and the largest international space science project in U.S. history. All the observatory’s flight hardware is now complete, however, the issues brought to light with the spacecraft element are prompting us to take the necessary steps to refocus our efforts on the completion of this ambitious and complex observatory.”
NASA also announced that it is establishing an external Independent Review Board (IRB) chaired by Thomas Young – a highly-respected NASA and industry veteran who has a long history of chairing advisory committees and analyzing organizational and technical issues. The IRB findings, along with the SRB data, will be considered by NASA to set a more specific launch date, and will be presented to Congress this summer.
In the meantime, NASA and the European Space Agency (ESA) will be setting a new launch readiness date for the Ariane 5 rocket that will bring the JWST into space. Once a launch date is set, NASA will also be providing a cost estimate that may exceed the $8 billion budget cap established by Congress in 2011. This too is in keeping with the GAO’s report, which predicted cost overruns.
For those who have been following the JWST’s development, this news should come as no surprise. Due to its complexity and the need for extensive testing, the launch of the JWST has been delayed several times in recent years. In addition, the final phase consists of some of the most challenging work, where the 6.5-meter telescope and science payload element are being joined with the spacecraft element to complete the observatory.
In addition, the science team also needs to ensure that the observatory can be folded up to fit inside the Ariane 5 rocket that will launch it into space. They also need to ensure that it will unfold again once it reaches space, deploying its sunshield, mirrors and primary mirror. Beyond that, there are also the technical challenges of building a complex observatory that was created here on Earth, but designed to operate in space.
Not only does all of this represent a very technically-challenging feet, it is the first time that any space telescope has had to perform it. Already, the JWST has completed an extensive range of tests to ensure that it will reach its orbit roughly 1.6 million km (1 million mi) from Earth. And while delays can be discouraging, they also increase the likelihood of mission success.
As Thomas Zurbuchen, the associate administrator for NASA’s Science Mission Directorate, stated:
“Considering the investment NASA and our international partners have made, we want to proceed systematically through these last tests, with the additional time necessary, to be ready for a May 2020 launch.”
The next step in testing will take several months, and will consist of the spacecraft element undergoing tests to simulate the vibrational, acoustic and thermal environments it will experience during its launch and operations. Once complete, the project engineers will integrate and test the fully assembled observatory and verify that all its components work together properly.
And then (fingers crossed!) this ambitious telescope will finally be ready to take to space and start collecting light. In so doing, scientists from all around the world hope to shed new light on some of the most fundamental questions of science – namely, how did the Universe evolve, is their life in our Solar System beyond Earth, are their habitable worlds beyond our Solar System, and are there other civilizations out there?
Bottom line, NASA remains committed to deploying the James Webb Space Telescope. So even if the answers to these questions are delayed a little, they are still coming!
Further Reading: NASA
Once deployed, the James Webb Space Telescope (JWST) will be the most powerful telescope ever built. As the spiritual and scientific successor to the Hubble, Spitzer, and Kepler space telescopes, this space observatory will use its advanced suite of infrared instruments to the look back at the earliest stars and galaxies, study the Solar System in depth, and help characterize extra-solar planets (among other things).
Unfortunately, the launch of the JWST has been subject to multiple delays, with the launch date now set for some time in 2019. Luckily, on Thursday, March 8th, engineers at the Northrop Grumman company headquarters began the final step in the observatory’s integration and testing. Once complete, the JWST will be ready to ship to French Guiana, where it will be launched into space.
This final phase consisted of removing the combined optics and science instruments from their shipping containers – known as the Space Telescope Transporter for Air, Road and Sea (STTARS) – which recently arrived after being testing at NASA’s Johnson Space Center in Houston. This constitutes half the observatory, and includes the telescope’s 6.5 meter (21.3 foot) golden primary mirror.
The science payload was also tested at NASA’s Goddard Space Flight Center last year to ensure it could handle the vibrations associated with space launches and the temperatures and vacuum conditions of space. The other half of the observatory consists of the integrated spacecraft and sunshield, which is in the final phase of assembly at the Northrop Grumman company headquarters.
These will soon undergo a launch environment test to prove that they are ready to be combined with the science payload. Once both halves are finished being integrated, addition testing will be performed to guarantee the fully assembled observatory can operate at the L2 Earth-Sun Lagrange Point. As Eric Smith, the program director for the JWST at NASA Headquarters, said in a recent NASA press statement:
“Extensive and rigorous testing prior to launch has proven effective in ensuring that NASA’s missions achieve their goals in space. Webb is far along into its testing phase and has seen great success with the telescope and science instruments, which will deliver the spectacular results we anticipate.”
These final tests are crucial to ensuring that that the observatory deploys properly and can operate once it is in space. This is largely because of the telescope’s complicated design, which needs to be folded in order to fit inside the Ariane 5 rocket that it will carry it into space. Once it reaches its destination, the telescope will have to unfold again, deploying its sunshield, mirrors and primary mirror.
Not only does all of this represented a very technically-challenging feet, it is the first time that any space telescope has had to perform it. Beyond that, there are also the technical challenges of building a complex observatory that is designed to operate in space. While the JWST’s optics and science instruments were all built at room temperature here on Earth, they had to be designed to operate at cryogenic temperatures.
As such, its mirrors had to be precisely polished and formed that they would achieve the correct shape once they cool in space. Similarly, its sunshield will be operating in a zero gravity environment, but was built and tested here on Earth where the gravity is a hefty 9.8 m/s² (1 g). In short, the James Webb Space Telescope is the largest and most complex space telescope ever built, and is one of NASA’s highest priority science projects.
It is little wonder then why NASA has had to put the JWST through such a highly-rigorous testing process. As Smith put it:
“At NASA, we do the seemingly impossible every day, and it’s our job to do the hardest things humankind can think of for space exploration. The way we achieve success is to test, test and retest, so we understand the complex systems and verify they will work.”
Knowing that the JWST is now embarking on the final phase of its development – and that its engineers are confident it will perform up to task – is certainly good news. Especially in light of a recent report from the US Government Accountability Office (GAO), which stated that more delays were likely and that the project would probably exceed its original budget cap of $8 billion.
As the report indicated, it is the final phase of integration and testing where problems are most likely to be found and schedules revised. However, the report also stated that “Considering the investment NASA has made, and the good performance to date, we want to proceed very systematically through these tests to be ready for a Spring 2019 launch.”
In other words, there is no indication whatsoever that Congress is considering cancelling the project, regardless of further delays or cost overruns. And when the JWST is deployed, it will use its 6.5 meter (21-foot) infrared-optimized telescopes will search to a distance of over 13 billion light years, allow astronomers to study the atmospheres of Solar Planets, exoplanets, and other objects within our Solar System.
So while the JWST may not make its launch window in 2019, we can still expect that it will be taking to space in the near future. And when it does, we can also expect that what it reveals about our Universe will be mind-blowing!
Further Reading: NASA
When the James Webb Space Telescope takes to space, some tremendous scientific discoveries are expected to result. As the spiritual and scientific successor to the Hubble, Spitzer, and Kepler Space Telescopes, this space observatory will use its advanced suite of infrared instruments to the look back at the early Universe, study the Solar System, and help characterize extra-solar planets.
Unfortunately, the launch of this mission has been delayed several times now, with the launch date now set for some time in 2019. And based on the amount of work NASA needs to do complete the JWST before launch, the Government Accountability Office (GAO) believes that more delays are coming and believes that the project is likely to exceed the cost cap set by Congress in 2011 at $8 billion.
Part of the problem is that all the remaining schedule reserve – the extra time set aside in the event of delays or unforeseen risks – was recently used to address technical issues. These include the “anomalous readings” detected from the telescope during vibration testing back in December 2016. NASA responded to this by giving the project up to 4 months of schedule reserve by extending the launch window.
However, in 2017, NASA delayed the launch window again by 5 months, from October 2018 to a between March and June 2019. This delay was requested by the project team, who indicated that they needed to address lessons learned from the initial folding and deployment of the observatory’s sunshield. As Eric Smith, the program director for the James Webb Space Telescope at NASA Headquarters, explained to Congress at the time:
“Webb’s spacecraft and sunshield are larger and more complex than most spacecraft. The combination of some integration activities taking longer than initially planned, such as the installation of more than 100 sunshield membrane release devices, factoring in lessons learned from earlier testing, like longer time spans for vibration testing, has meant the integration and testing process is just taking longer. Considering the investment NASA has made, and the good performance to date, we want to proceed very systemmatically through these tests to be ready for a Spring 2019 launch.”
Given the remaining integration and test work that lies ahead, more delays are expected. According to the GAO, it is this phase where problems are most likely to be found and schedules revised. Coupled with the fact that only 1.5 months of schedule reserves remain until the end of the launch window, they anticipate that additional launch delays are likely, which will also require budget increases.
Initially, the budget estimates that were set by Congress indicated that the observatory would cost $1.6 billion and would launch by 2011, with an overall cost cap set at $8 billion. However, NASA has revised the budget multiple times since then (in conjunction with the multiple delays) and estimates that the budget for a 2019 launch window would now be $8.8 billion.
Once deployed, the JWST will be the most powerful space telescope ever built and will serve thousands of astronomers worldwide. As a collaborative project between NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA), it also representative of the new era of international cooperation. But by far, the most impressive thing about this mission is the scientific discoveries it is expected to make.
It’s 6.5 meter (21-foot) infrared-optimized telescopes will search to a distance of over 13 billion light years, allowing it to study the first stars and galaxies that formed. It will also allow astronomers to study the atmospheres of Solar Planets and exoplanets and other objects within our Solar System. As such, and delays and cost overruns in the project are cause for concern.
In the meantime, the project’s Standing Review Board will conduct an independent review in early 2018 to determine if the June 2019 launch window can still be met. With so many experiments and surveys planned for the telescope, it would be no exaggeration to say that a lot is riding on its successful completion and deployment. Best of luck passing review James Webb Space Telescope!
Further Reading: Government Accountability Office
With every passing year, more and more extra-solar planets are discovered. To make matters more interesting, improvements in methodology and technology are allowing for the discovery of more planets within individual systems. Consider the recent announcement of a seven-planet system around the red dwarf star known as TRAPPIST-1. At the time, this discovery established the record for most exoplanets orbiting a single star.
Well move over TRAPPIST-1! Thanks to the Kepler Space Telescope and machine learning, a team from Google AI and the Harvard-Smithsonian Center of Astrophysics (CfA) recently discovered an eighth planet in the distant star system of Kepler-90. Known as Kepler -90i, the discovery of this planet was made possible thanks to Google algorithms that detected evidence of a weak transit signal in the Kepler mission data.
The study which describes their findings, titled “Identifying Exoplanets with Deep Learning: A Five Planet Resonant Chain Around Kepler-80 and an Eight Planet Around Kepler-90“, recently appeared online and has been accepted for publication in The Astronomical Journal. The research team consisted of Christopher Shallue of Google AI and Andrew Vanderburg of the University of Texas and the CfA.
Kepler-90, a Sun-like star, is located roughly 2,545 light-years from Earth in the constellation Draco. As noted, previous surveys had indicated the existence of seven planets around the star, a combination of terrestrial (aka. rocky) planets and gas giants. But after using a Google algorithm created to search through Kepler data, the research team confirmed that the signal of a another closer-orbiting planet lurked within the data.
The Kepler mission relies on the Transit Method (aka. Transit Photometry) to discern the presence of planets around brighter stars. This consists of observing stars for periodic dips in brightness, which are an indication that a planet is passing in front of the star (i.e. transiting) relative to the observer. For the sake of their study, Shallue and Vanderburg trained a computer to read light-curves recorded by Kepler and determine the presence of transits.
This artificial “neural network” sifted through Kepler data and found weak transit signals that indicated the presence of a previously-missed planet around Kepler-90. This discovery not only indicated that this system is very much like our own, it also confirms the value of using artificial intelligence to mine archival data. While machine learning has been used to search Kepler data before, this research demonstrates that even the weakest signals can now be discerned.
As Paul Hertz, director of NASA’s Astrophysics Division in Washington, said in a recent NASA press release:
“Just as we expected, there are exciting discoveries lurking in our archived Kepler data, waiting for the right tool or technology to unearth them. This finding shows that our data will be a treasure trove available to innovative researchers for years to come.”
This newly-discovered planet, known as Kepler-90i, is a rocky planet that is comparable in size to Earth (1.32 ± 0.21 Earth radii) that orbits its star with a period of 14.4 days. Given its close proximity to its star, this planet is believed to experience extreme temperatures of 709 K (436 °C; 817 °F) – making it hotter than Mercury’s daytime high of 700 K (427 °C; 800 °F).
As a senior software engineer with Google’s research team Google AI, Shallue came up with the idea to apply a neural network to Kepler data after learning that astronomy (like other branches of science) is becoming rapidly a “big data” concern. As the technology for data collection becomes more advanced, scientists find themselves being inundated with data sets of ever-increasing size and complexity. As Shallue explained:
“In my spare time, I started googling for ‘finding exoplanets with large data sets’ and found out about the Kepler mission and the huge data set available. Machine learning really shines in situations where there is so much data that humans can’t search it for themselves.”
The Kepler mission, in its first four-years in operation, accumulated a dataset that consisted of 35,000 possible planetary transit signals. In the past, automated tests and sometimes visual inspections were used to verify the most promising signals in the data. However, the weakest signals were often missed with these methods, leaving dozens or even hundreds of planets unaccounted for.
Looking to improve on this, Shallue teamed up Andrew Vanderburgh – a National Science Foundation Graduate Research Fellow and NASA Sagan Fellow – to see if machine learning could mine the data and turn up more signals. The first step consisted of training a neural network to identify transiting exoplanets using a set of 15,000 previously-vetted signals from the Kepler exoplanet catalogue.
In the test set, the neural network correctly identified true planets and false positives with a 96% accuracy rate. Having demonstrated that it could recognize transit signals, the team then directed their neural network to search for weaker signals in 670 star systems that already had multiple known planets. These included Kepler-80, which had five previously-known planets, and Kepler-90, which had seven. As Vanderburg indicated:
“We got lots of false positives of planets, but also potentially more real planets. It’s like sifting through rocks to find jewels. If you have a finer sieve then you will catch more rocks but you might catch more jewels, as well.”
The sixth planet in Kepler-80 is known as Kepler-80g, an Earth-sized planet that is in a resonant chain with its five neighboring planets. This occurs when planets are locked by their mutual gravity into an extremely stable system, similar to what TRAPPIST-1’s seven planets experience. Kepler-90i, on the other hand, is an Earth-sized planet that experiences Mercury-like conditions and orbits outside of 90b and 90c.
In the future, Shallue and Vanderburg plan to apply their neural network to Kepler’s full archive of more than 150,000 stars. Within this massive data set, many more planets are likely to be lurking, and quote possibly within multi-planetary systems that have already been surveyed. In this respect, the Kepler mission (which has already been invaluable to exoplanet research) has shown that it has a lot more to offer.
As Jessie Dotson, Kepler’s project scientist at NASA’s Ames Research Center, put it:
“These results demonstrate the enduring value of Kepler’s mission. New ways of looking at the data – such as this early-stage research to apply machine learning algorithms – promises to continue to yield significant advances in our understanding of planetary systems around other stars. I’m sure there are more firsts in the data waiting for people to find them.”
Naturally, the fact that a Sun-like star is now known to have a system of eight planets (like our Solar System), there are those who wonder if this system could be a good bet for finding extra-terrestrial life. But before anyone get’s too excited, it is worth noting that Kepler-90s planets all orbit rather closely to the star. It’s outermost planet, Kepler-90h, orbits at a similar distance to its star as Earth does to the Sun.
The discovery of an eighth planet around another star also means there’s a system out there that rivals the Solar System in total number of planets. Maybe it’s time we reconsidered the 2006 IAU decision – you know, the one where Pluto was “demoted”? And while we’re at it, perhaps we should fast-track Ceres, Eris, Haumea, Makemake, Sedna and the rest for planethood. Otherwise, how else do we plan on maintaing our record?
In the future, similar machine learning processes are likely to be applied to next-generation exoplanet-hunting missions, like the Transiting Exoplanet Survey Satellite (TESS) and the James Webb Space Telescope (JWST). These missions are scheduled to launch in 2018 and 2019, respectively. And in the meantime, there are sure to be many more revelations coming from Kepler!
Welcome all to the first in our series on Exoplanet-hunting methods. Today we begin with the most popular and widely-used, known as the Transit Method (aka. Transit Photometry).
For centuries, astronomers have speculated about the existence of planets beyond our Solar System. After all, with between 100 and 400 billion stars in the Milky Way Galaxy alone, it seemed unlikely that ours was the only one to have a system of planets. But it has only been within the past few decades that astronomers have confirmed the existence of extra-solar planets (aka. exoplanets).
Astronomers use various methods to confirm the existence of exoplanets, most of which are indirect in nature. Of these, the most widely-used and effective to date has been Transit Photometry, a method that measures the light curve of distant stars for periodic dips in brightness. These are the result of exoplanets passing in front of the star (i.e. transiting) relative to the observer.
These changes in brightness are characterized by very small dips and for fixed periods of time, usually in the vicinity of 1/10,000th of the star’s overall brightness and only for a matter of hours. These changes are also periodic, causing the same dips in brightness each time and for the same amount of time. Based on the extent to which stars dim, astronomers are also able to obtain vital information about exoplanets.
For all of these reasons, Transit Photometry is considered a very robust and reliable method of exoplanet detection. Of the 3,526 extra-solar planets that have been confirmed to date, the transit method has accounted for 2,771 discoveries – which is more than all the other methods combined.
One of the greatest advantages of Transit Photometry is the way it can provide accurate constraints on the size of detected planets. Obviously, this is based on the extent to which a star’s light curve changes as a result of a transit. Whereas a small planet will cause a subtle change in brightness, a larger planet will cause a more noticeable change.
When combined with the Radial Velocity method (which can determine the planet’s mass) one can determine the density of the planet. From this, astronomers are able to assess a planet’s physical structure and composition – i.e. determining if it is a gas giant or rocky planet. The planets that have been studied using both of these methods are by far the best-characterized of all known exoplanets.
In addition to revealing the diameter of planets, Transit Photometry can allow for a planet’s atmosphere to be investigated through spectroscopy. As light from the star passes through the planet’s atmosphere, the resulting spectra can be analyzed to determine what elements are present, thus providing clues as to the chemical composition of the atmosphere.
Last, but not least, the transit method can also reveal things about a planet’s temperature and radiation based on secondary eclipses (when the planet passes behind it’s sun). On this occasion, astronomers measure the star’s photometric intensity and then subtract it from measurements of the star’s intensity before the secondary eclipse. This allows for measurements of the planet’s temperature and can even determine the presence of clouds formations in the planet’s atmosphere.
Transit Photometry also suffers from a few major drawbacks. For one, planetary transits are observable only when the planet’s orbit happens to be perfectly aligned with the astronomers’ line of sight. The probability of a planet’s orbit coinciding with an observer’s vantage point is equivalent to the ration of the diameter of the star to the diameter of the orbit.
Only about 10% of planets with short orbital periods experience such an alignment, and this decreases for planets with longer orbital periods. As a result, this method cannot guarantee that a particular star being observed does indeed host any planets. For this reason, the transit method is most effective when surveying thousands or hundreds of thousands of stars at a time.
It also suffers from a substantial rate of false positives; in some cases, as high s 40% in single-planet systems (based on a 2012 study of the Kepler mission). This necessitates that follow-up observations be conducted, often relying on another method. However, the rate of false positives drops off for stars where multiple candidates have been detected.
While transits can reveal much about a planet’s diameter, they cannot place accurate constraints on a planet’s mass. For this, the Radial Velocity method (as noted earlier) is the most reliable, where astronomers look for signs of “wobble” in a star’s orbit to the measure the gravitational forces acting on them (which are caused by planets).
In short, the transit method has some limitations and is most effective when paired with other methods. Nevertheless, it remains the most widely-used means of “primary detection” – detecting candidates which are later confirmed using a different method – and is responsible for more exoplanet discoveries than all other methods combined.
Examples of Transit Photometry Surveys:
Transit Photometry is performed by multiple Earth-based and space-based observatories around the world. The majority, however, are Earth-based, and rely on existing telescopes combined with state-of-the-art photometers. Examples include the Super Wide Angle Search for Planets (SuperWASP) survey, an international exoplanet-hunting survey that relies on the Roque de los Muchachos Observatory and the South African Astronomical Observatory.
There’s also the Hungarian Automated Telescope Network (HATNet), which consists of six small, fully-automated telescopes and is maintained by the Harvard-Smithsonian Center for Astrophysics. The MEarth Project is another, a National Science Foundation-funded robotic observatory that combines the Fred Lawrence Whipple Observatory (FLWO) in Arizona with the Cerro Tololo Inter-American Observatory (CTIO) in Chile.
Then there’s the Kilodegree Extremely Little Telescope (KELT), an astronomical survey jointly administered by Ohio State University, Vanderbilt University, Lehigh University, and the South African Astronomical Society (SAAO). This survey consists of two telescopes, the Winer Observatory in southeastern Arizona and the Sutherland Astronomical Observation Station in South Africa.
In terms of space-based observatories, the most notable example is NASA’s Kepler Space Telescope. During its initial mission, which ran from 2009 to 2013, Kepler detected 4,496 planetary candidates and confirmed the existence of 2,337 exoplanets. In November of 2013, after the failure of two of its reaction wheels, the telescope began its K2 mission, during which time an additional 515 planets have been detected and 178 have been confirmed.
The Hubble Space Telescope also conducted transit surveys during its many years in orbit. For instance, the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS) – which took place in 2006 – consisted of Hubble observing 180,000 stars in the central bulge of the Milky Way Galaxy. This survey revealed the existence of 16 additional exoplanets.
Other examples include the ESA’s COnvection ROtation et Transits planétaires (COROT) – in English “Convection rotation and planetary transits” – which operated from 2006 to 2012. Then there’s the ESA’s Gaia mission, which launched in 2013 with the purpose of creating the largest 3D catalog ever made, consisting of over 1 billion astronomical objects.
In March of 2018, the NASA Transiting Exoplanet Survey Satellite (TESS) is scheduled to be launched into orbit. Using the transit method, TESS will detect exoplanets and also select targets for further study by the James Webb Space Telescope (JSWT), which will be deployed in 2019. Between these two missions, the confirmation and characterization or many thousands of exoplanets is anticipated.
Thanks to improvements in terms of technology and methodology, exoplanet discovery has grown by leaps and bounds in recent years. With thousands of exoplanets confirmed, the focus has gradually shifted towards the characterizing of these planets to learn more about their atmospheres and conditions on their surface.
In the coming decades, thanks in part to the deployment of new missions, some very profound discoveries are expected to be made!