7 Earth-Sized Worlds Discovered Orbiting Nearby Star

Artist's concept of the surface of TRAPPIST1-f.

Artist’s concept of the surface of TRAPPIST1-f. – Credit: NASA/JPL-Caltech

NASA held a press conference today, announcing an exciting new discovery: A record-breaking seven Earth-sized planets have been discovered orbiting a star located about 40 light years from Earth. Three of these planets are firmly located within what’s called the habitable zone–the area around a star that is likely to have rocky planets with liquid water.

The star is named TRAPPIST-1 (also known as 2MASS J23062928-0502285). It’s an ‘ultra-cool dwarf’ star, with approximately 8% of the mass and 11% of the radius of our Sun. Size-wise, this is approximately the difference between a basketball and a golfball.

The seven plants surrounding TRAPPIST-1 orbit much closer to their star than Earth does to the Sun. As well, these exoplanets are much closer to each other than the planets in our own system. You could stand on one of these planets and see the next closest one with a similar type of view that we have with the Moon here on Earth, and you could clearly make out the disc-shape of many of the other planets rather than mere points of light.

The discoveries were made using data from the Spitzer Space Telescope, which was launched in 2003. Although Spitzer wasn’t specifically designed to observe exoplanets, the suite of instruments it carries allows it to discover exoplanets in the same manner that the Kepler spacecraft uses. These observatories can discover exoplanets by precisely measuring dips in the light emitted from a star that coincides with a planet orbiting in-between that star and our vantage point and blocking a portion of the light that we can measure. Continued observations can determine orbital periods, distance from the star, and the number of exoplanets in a system. This data can be used to plot habitable zones.

During the press conference, the team stated that they had preliminary mass measurements for six of the planets, and they believe that one is likely to have a water-rich composition.

Artist's concept shows what each of the TRAPPIST-1 planets may look like, based on available data about their sizes, masses and orbital distances.

Artist’s concept shows what each of the TRAPPIST-1 planets may look like, based on available data about their sizes, masses and orbital distances. – Credit: NASA/JPL-Caltech

There currently isn’t a system for naming exoplanets in the way that bodies like asteroids are named, so they’re simply provided with alphabetic designations appended to their host stars’ name, with the designation ‘b’ being the closest to the star.

These planets orbit so close to their star that they’re likely tidally-locked in the same manner that the Moon is to the Earth. These planets would have permanent day and night sides.

One of the planets, Trappist-1c, is very similar in size to Earth and receives about the same amount of light as Earth receives from the Sun. It could very well have temperatures similar to those we have on Earth. Trappist-1f has a 9-day orbit and receives about as much light as Mars does. Trappist-1g is the largest planet in the system with an estimated radius 13% larger than Earth.

All of the planets are within a few times the distance between the Earth and the Moon of each other, and being so close to their star their orbits (their years) are about 1.5 Earth days for the closest planet and 20 days for the furthest.

Concept art for TRAPPIST-1 and its seven Earth-sized exoplanets.

Concept art for TRAPPIST-1 and its seven Earth-sized exoplanets. – Credit: NASA/JPL-Caltech

The next step, which is already ongoing, is to study their atmospheres and to look for water. This can be accomplished using a technique called transmission spectroscopy. We have observatories that can do this now, such as the Hubble Space Telescope, and the future James Webb Space Telescope (JWST) will be able to push these capabilities even further. JWST will be able to look for greenhouse gas content and determine the surface temperatures of these planets, as well as detect gases that are produced by life. It’s expected that the first cycle of observations of the JWST will include the TRAPPIST-1 system.

Thomas Zurbuchen, associate administrator of the agency’s Science Mission Directorate in Washington, referred to our moment in time as “the gold rush phase of exoplanet discovery.”  It was just in 1995 that the first exoplanet was discovered, he explained, and that thousands have been discovered since.

Following the announcement, the panel held a Q&A session. During the course of their answers, they explained that there was no indication of these planets having moons, but that if water was present there would be tidal activity resulting from the other planets. They said they expect substantial progress in determining the atmospheric composition of these exoplanets within the next 5 years, utilizing the Hubble Space Telescope and the James Webb Space Telescope after it begins operations in 2018. JWST’s transmission spectroscopy will cover the range needed to determine the potential for life.

One member asked if any attempts have been made to listen to the system with SETI-style instruments, to which there was a reply that SETI itself had listened to the system but hadn’t picked-up any signals.

One of the most interesting answers came from Zurbuchen, when he was asked when we could expect to construct a craft that could journey to this system. Rather than give an estimate in the number of years in the future we could expect such capabilities, he answered with the estimated “number of miracles” that are required before we get there. He explained that the JWST required 10 miracles to become possible. He likened the construction of a craft that could explore TRAPPIST-1 as requiring “100 miracles”, but that we shouldn’t be dissuaded, that to get there you have to “start inventing your way forward.” Some of the “miracles” require advancements in propulsion systems and radiation-protection, and that the good news was that substantial work is already being accomplished towards about 5-10 of these miracles. He said it’s about “leaning forward” and “not backing up”.

Discoveries like these are constant reminders of just how big and amazing our Universe is. We’re reminded that the night sky isn’t just full of points of light, but worlds, perhaps some of which might be very similar to our own.

A poster advertising a hypothetical planet-hopping trip in the Trappist-1 system

A poster advertising a hypothetical planet-hopping trip in the Trappist-1 system – Credit: NASA-JPL/Caltech

Clyde Tombaugh Discovers Pluto

*click* ….. *click* …. *click* …. *click*

On this day in 1930, a 24-year-old man named Clyde Tombaugh was squinting into the Lowell Observatory’s Zeiss Blink microscope. The unique device, also known as a blink comparator, held two photographic plates that each contained the image of a star field taken the previous month–the images showing the same section of sky, taken a few days apart. Tombaugh could rapidly switch between the two images by rotating a dial, allowing him to quickly compare the images and watch for any variations between the two that would indicate a body moving more rapidly than the background stars (eg. planets, asteroids, etc.).

*click* ….. *click*

Late into that February afternoon, a subtle difference between the two images caught his eye.

Animation comparing Tombaugh's star fields.

Can you spot Pluto?  Click on the image to see a version with Pluto identified.   Image Credit: National Air & Space Museum

 

*click* … *click* … *click* .. *click* . *click* *click*

He spent 45 minutes comparing the two images. Convinced of his findings, he contacted his supervisors. Over the next couple of weeks, the observatory focused its attention to the object before confirming Tombaugh’s discovery. On May 1st, 1930, a new planet was introduced to the world: Pluto.

And of course, in 2015, we got to see Pluto in a way that Mr. Tombaugh himself could only have imagined.

NASA’s New Horizons spacecraft captured this high-resolution enhanced color view of Pluto on July 14, 2015.

NASA’s New Horizons spacecraft captured this high-resolution enhanced color view of Pluto on July 14, 2015.        Source: NASA

Ceres–Either the Most or Second-Most Popular Dwarf Planet

It has been nearly a decade since the International Astronomical Union (IAU) formally defined the word ‘planet’, resulting in the reclassification of Pluto as a ‘dwarf planet’. Some people still remain upset about the decision, considering the new classification as a demotion. If you roll with the kinds of people that I do, battle-lines have been drawn around the issue and many a friendship have been lost in the process. I don’t want to rekindle those debates (this is likely inevitable, however, as Pluto will be in the news quite a bit in the coming months as New Horizons is finally about to have its encounter with the dwa… whatever-you-want-to-call-it), so let’s take a look at a dwarf planet that appears to have finally found comfort in its classification: Ceres.

Color view of Ceres as imaged by Hubble in 2004 - Credit: NASA, ESA, J. Parker (Southwest Research Institute), P. Thomas (Cornell University), L. McFadden (University of Maryland, College Park), and M. Mutchler and Z. Levay (STScI)

Color view of Ceres as imaged by Hubble in 2004 – Credit: NASA, ESA, J. Parker (Southwest Research Institute), P. Thomas (Cornell University), L. McFadden (University of Maryland, College Park), and M. Mutchler and Z. Levay (STScI)

If you thought Pluto’s designation was complicated and controversial, just wait until you Ceres’s story.

Ceres has had a bit of an identity crisis of its own. Italian astronomer Giuseppe Piazzi discovered Ceres on New Years Day, 1801. He at first thought it was a star, but observed its movements against the stellar backdrop over the course of a few days and determined it to be a planet. He took a conservative approach in his announcement however, by referring to it as a comet.

I have announced this star as a comet, but since it shows no nebulosity, and moreover, since it had a slow and rather uniform motion, I surmise that it could be something better than a comet. However, I would not by any means advance publicly this conjecture. – Giuseppe Piazzi in a letter to fellow Italian astronomer Barnaba Oriani

With the help of other astronomers and using a method for calculating orbits developed by Carl Friedrich Gauss, it was confirmed that the object was not a comet, but in fact some sort of small planet. German astronomer Johann Bode had been promoting his hypothesis that planets orbited their host stars at distances that could predicted by mathematics. This hypothesis predicted a planet should exist between Mars and Jupiter. When Bode heard news of Piazzi’s discovery of an object at precisely that location, he rushed to announce that the missing planet had been located and even went as far as to name it himself. The name he gave: Juno. Piazzi, however, had taken the liberty as the new planet’s discoverer to give it the name ‘Ceres Ferdinandea’, honoring the patron goddess of Sicily and King Ferdinand of Bourbon. Piazzi rightfully objected to Bode’s stake on naming rights:

“If the Germans think they have the right to name somebody else’s discoveries they can call my new star the way they like: as for me I will always keep it the name of Cerere and I will be very obliged if you and your colleagues will do the same.” Piazzi in a letter to prominent astronomer and editor of scientific journals, Franz Xaver von Zach.

Piazzi’s name ultimately won out, though it was shortened to its currently-accepted name: Ceres.

"Giuseppe Piazzi" by F. Bordiga - Image from Smithsonian Institute Library

“Giuseppe Piazzi” by F. Bordiga – Image from Smithsonian Institute Library

After more objects were discovered orbiting in the same area, Sir William Herschel, in 1802, labeled these new objects, including Ceres, as asteroids (though the term asteroid, which means “star-like”, wasn’t commonly accepted until the early 1900s).

So thus, Ceres became the first, and largest, of the asteroids that orbit between Mars and Jupiter in a loose collection that we collectively refer to as the asteroid belt. But Ceres’s identity crisis wasn’t over just yet. Ceres was king of the asteroids until 2006, when that controversial IAU reclassified it as a dwarf planet. 1

From star, to comet, to planet, to asteroid, and finally to dwarf planet, Ceres looks to Pluto and remarks, “Psh… and you think you had it bad.”

Now that this introduction is out of the way, stay tuned for more information about Ceres. I’ll tell you about this fascinating world and get you up to speed on NASA’s Dawn spacecraft that will be arriving at Ceres in March of this year.

Animation of Ceres as viewed by the Dawn spacecraft on January 13, 2015. - Source: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI

Animation of Ceres as viewed by the Dawn spacecraft on January 13, 2015. – Source: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI

(Much of the information in this post came from Giuseppe Piazzi and the Discovery of Ceres, G. Foderà Serio, A. Manara, and P. Sicoli, published in Asteroids III by the University of Arizona Press)


  1. Since Pluto’s reclassification from planet to dwarf planet was viewed by many as a demotion, I wonder if it’s safe to refer to Ceres’s reclassification from asteroid to dwarf planet as a promotion.

A Space Discovery Milestone, as Kepler Confirms 1000th Exoplanet

Kepler Mission Logo

Kepler Mission logo

It was just a few years ago, and I was excitedly reporting to you the first few exoplanets that the NASA Kepler space instrument was detecting and verifying. In fact, it was almost exactly 4 years ago today that I was telling you about confirmed exoplanet find number 9. That exoplanet, Kepler-10b, was the first confirmed find of a rocky world outside of our own solar system, and at the time was the smallest exoplanet ever discovered, at 1.4 times the diameter of Earth. Then, at the end of that year, I was telling you about the first exoplanet located by Kepler in the “habitable zone”. And in a short period of time, I was telling you about dozens of more exoplanets being confirmed, and mini-planetary systems, and exoplanets that orbit two different stars.

Well since then, Kepler’s been hard at work confirming exoplanet after exoplanet. Today, that count has reached a milestone:

NASA’s Kepler Marks 1,000th Exoplanet Discovery, Uncovers More Small Worlds in Habitable Zones

1,000 confirmed other worlds, orbiting other stars. Let me put that significance into perspective: if you were born in 1988 or earlier, you are the exoplanet generation, for 1988 was the year the first exoplanet was confirmed. I don’t know about you, but that fact really resonates with me. It proclaims to me that I live in a fantastic moment of human history. I was alive when Earthlings first knew for certain that there were planets outside of our own Solar system. And in less than three decades, we’ve found over 1,000 more. There are worlds out there, and we’re alive precisely at the time to first know it. And what’s even cooler, at least eight of those are roughly the same size as our own world and orbit their host star in what’s referred to as the habitable zone.

Artist's depiction of the 8 Earthlike planets confirmed by Kepler.

 

The Kepler mission will always be one of the most exciting for me personally, and is expected to confirm thousands more exoplanets over the coming years. What a time to be alive!

If this is as interesting to you as it is to me, here are a couple of other articles posted about Kepler discoveries that I think you’ll particularly appreciate:

Exciting Kepler News – Part 1: Mini-Planetary System

Exciting Kepler News – Part 2: New Circumbinary Planets

Kepler Finds First Earth-Sized Planets


NASA's State of the Solar System

Here’s an excellent infographic that details NASA’s current Solar System (and beyond!) spacecraft missions. It lists every craft NASA out exploring various bodies and their current status.

Click the image to make it a little bigger.

State of the Solar System infographic

State of the Solar System infographic

(Via)

 


Pioneer Non-Anomaly

Artist depiction of Pioneer spacecraft in deep space.

Artist depiction of Pioneer spacecraft in deep space. Image Credit: NASA

Pioneer 10 and 11 launched in 1972 and 1973, respectively, and were Earthkind’s  first explorers of the outer planets and emissaries to deep space.  Pioneer 10 became the first spacecraft to pass through the asteroid belt and observe Jupiter up-close, providing us with details of the gas giant’s interior, atmosphere, magnetic fields, and some of the most breath-taking images of Jupiter we had ever seen. Pioneer 11 wasn’t far behind, and after making its own observations of Jupiter, it went on to Saturn to open our eyes to the mighty ringed planet in the same way Pioneer 10 had done for Jupiter. (But this isn’t a story about the accomplishments of the Pioneer program; I’ll save that for another day.)

In addition to all of the data and images sent back, however, those two Pioneers also sent back a mystery. As early as 1980, it was noticed that the spacecrafts were experiencing an acceleration force toward the sun of .000000000874 m/s2 (meters per second, per second)1. To be clear, this does not mean the Pioneers are heading back towards the Sun. Pioneer 10 and 11 are cruising away from the Sun at a speed of around 132,000 kilometers per hour (82,000 miles per hour) and 175,000 kilometers (110,000 miles per hour), respectively, and this force is 10 billion times smaller than the acceleration we feel from the Earth’s gravitational pull. Nonetheless, the force is real and our instruments and techniques are precise enough to notice.

Many plausible causes were considered to explain the anomaly, including:

perturbations from the gravitational attraction of planets and smaller bodies in the solar system; radiation pressure, the tiny transfer of momentum when photons impact the spacecraft; general relativity; interactions between the solar wind and the spacecraft; possible corruption to the radio Doppler data; wobbles and other changes in Earth’s rotation; outgassing or thermal radiation from the spacecraft; and the possible influence of non-ordinary or dark matter.

In 1994, a thorough, long-term, collaborative study was undertaken to try and solve the anomaly. Initial results from that study were released in 1998, with a detailed analysis following in 2002. All known systematics were tested and calculated, yet that 8.74±1.33×10−10 m/s2 deceleration force2 remained. The origin of the anomaly was still unaccounted for, though the leading theory was that it was the result of anisotropic thermal radiation (don’t let the big words intimidate you, this just means heat was being radiated from the Pioneers in a certain direction). In 2004, another paper was published, proposing a deep space mission to solve the anomaly once-and-for-all.

But now, that expensive deep-space mission won’t be necessary, according to a paper just submitted by astrophysicist Slava Turyshev and his team of scientists and engineers, with thanks, in no small part, to The Planetary Society and its members.3

With funds provided by The Planetary Society, Turyshev and his team were able to collect and compile great volumes of data from the two Pioneer missions. The data had to come from a variety of different sources and came in any number of formats, media, and condition. According to Bruce Betts, Director of Projects at The Planetary Society:

“This was not an easy (or quick) task. These missions lasted for more than 30 years. Imagine all the people, computing formats, and hardcopy and electronic storage devices involved over that period, and you’ll start to get an idea of the problem.”

Boxes of Pioneer data tapes.

Boxes of data tapes from the Pioneer missions. Image Credit: The Planetary Society

Think of what you would have to go through if I handed you a 5.25″ floppy disk that contained… well, it couldn’t contain much compared to the amount of data we exchange today, but whatever it was, it was something you needed. Imagine trying to find the hardware to read the disk, and then the intermediary hardware and software that would be required to get the data from the disk onto one of today’s modern machines so you could even utilize it. If you consider how much technology has changed between now and floppy disks, you can only begin to imagine how much it has changed since the 1970s and how cumbersome compiling all of this data, let alone securing it, must have been. I digress.

Once Turyshev and his team were able to assemble the more-complete data picture, they were able to isolate the source of acceleration: that anisotropic thermal radiation. Again, Bruce Betts:

Why was the thermal emission from the spacecraft anisotropic and slowing the spacecraft down? First of all, because the Pioneer spacecraft were spin-stabilized and almost always pointed their big dishes towards Earth. Second of all, because two sources of thermal radiation (heat) were then on the leading side of the spacecraft. The nuclear power sources, more formally Radioisotope Thermoelectric Generators (RTG), emitted heat towards the back side of the dishes. When the dishes reflected or re-radiated this heat, it went in the direction of travel of the spacecraft. Also, the warm electronics box for the spacecraft was on the leading side of the spacecraft, causing more heat to spill that direction. Photon pressure, the same type of thing used in solar sailing, then preferentially pushed against the direction of travel, causing a tiny, but measurable, deceleration of the spacecraft – the Pioneer Anomaly.

At the end of the day, there are a few take-home lessons to be learned. First, Occam’s Razor proved itself once again (some of the suggestions to account for the Pioneer Anomaly were the need to invoke a new type of exotic physics). The second is that you can’t just apply Occam’s Razor and say that anisotropic thermal radiation is the simplest theory and therefore correct, you have to painstakingly collect all of the data needed to prove it — and more importantly, you have to have the experts that are willing to put forth the years decades of research to solve the mystery. Finally, you take in the account that this was made possible with the help of citizen scientists and those of us that contribute to furthering our understanding of the Universe, through means such as The Planetary Society4.

This new paper will undoubtedly generate more discussion about the Pioneer Anomaly and others will work to verify or disprove its results, but at this point it seems pretty safe to say that one of space physic’s mysteries is no more.


  1. 8.74±1.33×10−10 m/s2
  2. In physics, acceleration is a change in velocity over time. It does not only apply to an increase in speed. Traveling in your hot-rod sports car, as you step on the gas and race up to 100 miles per hour, you’re experiencing acceleration. When you notice a brick wall rapidly closing in from ahead of you and you stand on the brakes, you’re experiencing a negative acceleration. Acceleration is just a change from a constant velocity.
  3. Are you a member of The Planetary Society? I am. You should be, too! Sign up!
  4. Again, join!

F-1 Rocket Engine Recovery

They took rocket-grade kerosene and liquid oxygen, and turned it into 1.5 million pounds of thrust, 32 million horsepower, and made it possible to take the Apollo astronauts to the Moon. I’m talking about the Rocketdyne F-1 rocket engines used in the first stage of Saturn V — the only vehicle to take humans outside of low-Earth orbit.

Following launch, five F-1 engines would burn for about 2-and-one-half minutes, boosting the Saturn V and its payload to an altitude of nearly forty miles, and 55 miles downrange from Cape Kennedy. At that point, the first stage (S-1C) containing the F1 engines would separate from the rest of the Saturn V and fall back to Earth, crashing into the Atlantic Ocean where they would rest forever.

Separation of Apollo first stage from other two stages of the Saturn V.

Separation of the first (S-1C) stage containing the F-1 engines from the other two Saturn V stages, during Apollo 11.

(Image Credit: NASA)

At least, forever was how long we thought they would sit there….

Amazon.com founder, Jeff Bezos, recently announced that a “team of undersea pros” that he funded had found the most famous F-1 engines of all; the ones from Apollo 11 that launched humanity to the Moon, where the first humans would walk on another world. But finding them is just the start, Bezos Expeditions is planning on actually recovering one or more of the F-1s.

“We don’t know yet what condition these engines might be in – they hit the ocean at high velocity and have been in salt water for more than 40 years. On the other hand, they’re made of tough stuff, so we’ll see”, Bezos said in the announcement. He also pointed out that regardless of how long the engines have spent 14,000 feet below the surface of the Atlantic, they are still the sole property of NASA. He also stated that he had requested that NASA make available for display at the Museum of Flight in Seattle, Washington, the second F-1 his group manages to salvage (the first presumably would go to the Smithsonian).

NASA followed the announcement with a press release of their own, in which NASA Administrator Charles Bolden expressed his support for the project, and acknowledged the request to house a second (or the first, if the Smithsonian declines it) F-1 at Bezos’ requested facility.

“NASA does retain ownership of any artifacts recovered and would likely offer one of the Saturn V F-1 engines to the Smithsonian Institution’s National Air and Space Museum in Washington under long-standing arrangements with the institution as the holder of the national collection of aerospace artifacts.

“If the Smithsonian declines or if a second engine is recovered, we will work to ensure an engine or other artifacts are available for display at the Museum of Flight in Seattle, as Jeff requested in his correspondence with my office.”

As of yet, there hasn’t been an announced timeline, cost, or specific details released about the project; however, I personally suspect Bezos will have no problem pulling together the resources needed to tackle the feat.

Bezos ended the announcement with a quote that echoes my own heart when it comes to NASA’s ability to inspire:

NASA is one of the few institutions I know that can inspire five-year-olds. It sure inspired me, and with this endeavor, maybe we can inspire a few more youth to invent and explore.

Good luck, Bezos Industries. Thanks for taking the public treasure that NASA is and multiplying its inspiration for generations to come.


Exciting Kepler News – Part 2: New Circumbinary Planets

 There were two exciting Kepler (the NASA mission tasked with discovering planets outside of our solar system) news released yesterday. I’m covering them in two separate posts. This is Part 2; read Part 1.

The second exciting Kepler news release is one of the most interesting yet; in fact, this discovery confirmed the existence of an entirely new class of planetary system! Today, astronomers announced the discovery of two new “circumbinary” planet systems; these follow the first circumbinary planet system announced in September of last year, the planet Kepler-16b.

So what does circumbinary mean anyway, and why is it so interesting? Let me answer the first question, which should preclude the need to answer the second.

Scene from Star Wars Episode IV: A New Hope, showing binary stars from Tatooine.
Classic scene from Star Wars Episode IV: A New Hope, showing a dual sunset from the circumbinary planet, Tatooine.

A circumbinary planet is one that orbits not one, but two stars. When Kepler-16b was confirmed last Fall, it wasn’t clear whether we should expect many more circumbinary planets or if that system was just a fluke. With the discovery of these two new systems, it is becoming apparent that circumbinary planets are abundant.

What makes this interesting is that binary-star systems are abundant in our galaxy. From the report published in Nature:

The observed rate of circumbinary planets in our sample implies that more than ~1% of close binary stars have giant planets in nearly coplanar orbits, yielding a Galactic population of at least several million.

At least several million!

As for the planets themselves, they are both gas giants about the size of Saturn.  Kepler-34b orbits its binary-pair of Sun-like stars every 289 days, while the stars themselves orbit and eclipse each other every 28 days. Kepler-35b orbits its smaller pair of stars every 131 days, with the stars orbiting and eclipsing one another every 21 days.  The Kepler-34 and Kepler-35 systems lie in the constellation Cygnus, 4,900 and 5,400 light-years from Earth, respectively.


For more information, check out these links:

NASA Kepler News Release

The paper, published in Nature

The news release for Kepler-16b, the first circumbinary planet discovered


Exciting Kepler News – Part 1: Mini-Planetary System

 

There were two exciting Kepler (the NASA mission tasked with discovering planets outside of our solar system) news releases today. I’ll cover them in two separate posts. This is Part 1; stay tuned for Part 2.

KOI-961 Artist Concept

(Click to englarge / Image credit: NASA/JPL-Caltech)

Announced today was the discovery of the three smallest exoplanets (planets orbiting a star other than the Sun) ever discovered. These planets are orbiting a red dwarf star, currently1 named KOI-961 (KOI = Kepler Object of Interest). These planets are all smaller than our home planet, having a radius of .78, .73, and .57 that of Earth’s. (The smallest is about the size of Mars.) Though the planets are thought to be rocky, they orbit KOI-961 very closely, making them too hot to have any likelihood of being habitable.

The planets, currently 2 named KOI-961.01, KOI-961.02, and KOI-961.03, circle their host star at a fair clip, completing an orbit in less than two Earth-days. The star, KOI-961, has much less mass than our Sun. Its diameter is 1/6 the size of the Sun (which is only about 70% larger than Jupiter).

The discovery announced today came from a team of scientists, led by astronomers from the California Institute of Technology (Caltech). They made their discovery by analyzing publicly-released data from the Kepler mission. Studying KOI-961, they were able to greatly refine the preliminary estimated size of the red dwarf, and subsequently verify the presence of the three small exoplanets.

KOI-961 exoplanet comparisons

(Click to enlarge / Image Credit: NASA/JPL-Caltech)

If you’re interested in further details about how Caltech made the discovery, I highly recommend you read their press release.

So let’s take a step back and ponder about what this latest discovery means. Coupled with the many frequent previous Kepler discoveries, we’re starting to create a big picture in which planets are ubiquitous throughout the Universe. Red dwarfs are the most common type of star in at least our own galaxy, and if one red dwarf has a planetary system, it’s likely more do… maybe even most do. We’re discovering planets around different types of stars; those similar to the Sun and those considerably different. Planets of different sizes and compositions as well. Not just large gas giants with little hope for containing life, but smaller, rocky worlds. Other Earth-sized worlds. Other Earth-like orbits. Other… Earths.

The speed at which we’re making these otherworldly discoveries is astounding and encouraging. It wasn’t long ago, I sat wondering if there were other planets out there, beyond our solar system, and if they might be discovered in my life. Today, I’m overwhelmed trying to keep up with all of the new exoplanet discoveries!

This is an exciting era to live in.


  1. I say currently, because once Kepler exoplanets are confirmed, the star generally gets the designation Kepler followed by a number, and the exoplanets are named after the star, followed by a letter designation. For example, Kepler-22b orbits the star Kepler-22. The designation “b” indicates it was the second expolanet discovered in that system.
  2. See the first footnote!

Kepler Finds First Earth-Sized Planets

NASA just announced that the Kepler mission has discovered the first Earth-sized planets outside of our solar system.

The planets, Kepler-20e and Kepler-20f,  while Earth-sized and thought to be rocky, are not believed to be habitable. They are much too close to their Type G star, Kepler-20, and too hot to retain liquid water.  Kepler-20e has a radius about 13% smaller than the Earth, making it just slightly smaller than Venus, and whips around Kepler-20 in a mere 6.1 days. Kepler-20f has a radius 3% larger than that of the Earth, with its year being a still fast 19.6 days.  The Kepler-20 system is approximately 1,000 light years from Earth.

Read the NASA release for even more details.

The Kepler mission is playing out like the fairy-tale, Goldilocks and the Three Bears. By that, I mean that we’re closing in on those planets that are “just right” for harboring life. We’ve discovered large planets inside the habitable zone that lacked a rocky surface (Kepler-22b) and gas giants not unlike Jupiter. Today, we’re finding Earth-sized planets with a rocky terrain. We’re getting ever so close to discovering those “Goldilocks” planets, with the size, composition, and being within the habitable zone, that allow them to be habitable.  And with more than 2300 candidates out there still waiting to be verified by Kepler, and Kepler’s current rate of discovery, I believe the announcement of a goldilocks planet is just around the corner.

Earth-class Planets Line Up