What is the biggest known planet in the Universe?

What is the biggest known planet in the Universe?
VLT NACO image, taken in the Ks-band, of GQ Lupi. The feeble point of light to the right of the star is the newly found cold companion. It is 250 times fainter than the star itself and it located 0.73 arcsecond west. At the distance of GQ Lupi, this corresponds to a distance of roughly 100 astronomical units. North is up and East is to the left.   Credit:    ESO

VLT NACO image, taken in the Ks-band, of GQ Lupi. The feeble point of light to the right of the star is the newly found cold companion. It is 250 times fainter than the star itself and it located 0.73 arcsecond west. At the distance of GQ Lupi, this corresponds to a distance of roughly 100 astronomical units. North is up and East is to the left. Credit: ESO

If you would like to pledge your regular support, please follow the button above! Not sure what this is? Check the bottom of the article. Thank you so much for being a reader!

Our list of known planets and exoplanets unfortunately doesn’t extend much beyond our own Milky Way galaxy - to spot a planet, you need to be able to measure the light from an individual star and monitor it over time. You’re looking either for tiny flickers in the amount of light you receive, as a planet happens to pass in front of the star you’re watching, or you’re looking for there to be a little Doppler shift in the color of the star’s light, as the planets tug it slightly off center as they orbit.  Known by the names of the transit method and the Doppler shift method respectively, both of these require really careful observations over a significant amount of time, without the light from the star mixing with the light from other stars. This limits us pretty well to the stars within or surrounding our Milky Way.

Because the measurements required to spot planets must be so precise, generally the telescopes we send out to do these measurements only look at a small patch of the sky. So while I can give you our current high scoring planets, there’s no guarantee these will remain the all-time bests, if we point our telescopes in a new direction.

There is one fundamental limitation to how massive a planet can get - if you pack too much material into a planet, it will start to fuse elements in its core, and it formally becomes a star instead of a planet. This transition happens when the object is somewhere in the range of 13 to 80 times the mass of Jupiter, and is the point at which we typically start calling objects a brown dwarf star, orbiting another star, instead of a planet. The list of biggest planets can also change if we get better measurements. It's possible to learn that what we thought was a planet should really be called a brown dwarf, which then bumps that object off the list of biggest planets, and onto the list of known brown dwarfs.

This artist's conception illustrates what a "Y dwarf" might look like. Y dwarfs are the coldest star-like bodies known, with temperatures that can be even cooler than the human body. Image credit:  NASA/JPL-Caltech

This artist's conception illustrates what a "Y dwarf" might look like. Y dwarfs are the coldest star-like bodies known, with temperatures that can be even cooler than the human body. Image credit: NASA/JPL-Caltech

However, you can still have very large, fluffy planets, well before they get to this boundary of being a star. Most of the ones we know about are Jupiter like in style - massive, gaseous planets, orbiting distant stars. The easiest to find are hot Jupters - exoplanets which are not only bigger than Jupiter, they’re much closer into their star than Jupiter is to our Sun. Currently, the majority of the biggest, fluffiest planets are about twice the radius of Jupiter. Considering that you could stack 22 and a half Earths edge to edge to match the width of Jupiter, you’re looking at a planet so large, you could line up 45 Earths behind it, and not see any of them. These planets have the very pronounceable names of ROXs 42Bb, which is estimated to be about 2.5 times the size of Jupiter, or Kepler-13 Ab, which sits around 2.2 times the size of Jupiter.

There are some larger ones, but these have preliminary estimates of their size, and may yet turn out to be brown dwarfs. The current record holder is a planet orbiting a star known as GQ Lupi, and estimates place it at somewhere around 4 times larger than Jupiter. This particular object is so large that our theoretical models of how it has formed are not particularly happy, and so the estimates on its size and mass are both pretty hazy. It is likely to remain a planet, but if it turns out that its mass is on the high end of our current estimates, it could wind up on a brown dwarf list. (This object is also extremely young, and will change and compress as it evolves.)

Artist's impression of the simultaneous stellar eclipse and planetary transit events on Kepler-1647.  Credits: Lynette Cook

Artist's impression of the simultaneous stellar eclipse and planetary transit events on Kepler-1647. Credits: Lynette Cook

These big fluffy planets are orbiting your default solar system - one with a single star, around which all the planets orbit.  If you have two stars (which isn’t that uncommon), it seems to be much harder to build very large planets. The largest planet known to circle two stars at once was only confirmed in 2016, and is almost identical to Jupiter in size. At “only” 22.5 Earths in size, it orbits its parent star once every three years.


What's this about Patreon? Patreon lets you pledge regular support for creators you enjoy. In the case of Astroquizzical, it's a per-article pledge, up to a limit that you specify. If you pledge above a certain amount, you'll get perks, like seeing these articles a day before they go live on the main site, or access to the materials I used to research the answers.

Astroquizzical is an ad-free site, and I'd like it to stay that way. Patreon will help pay for hosting costs, and you'll be supporting science communication with no paywall and no ads. Thank you so much for reading, for your support over the years, and here's to many more years of new and fun questions!


Have your own question? Feel free to ask! Or submit your questions via the sidebarFacebook, or twitter.

Sign up for the mailing list for updates & news straight to your inbox! Astroquizzical is now a bookCheck here for details & where to order!

Can Planets Bend Light?

Because large objects in space have an effect on light, can smaller objects do the same thing? Can something the size of the Earth also influence light and make it bend?
This artist's concept shows OGLE-2016-BLG-1195Lb, a planet discovered through a technique called microlensing. Image credit: 

This artist's concept shows OGLE-2016-BLG-1195Lb, a planet discovered through a technique called microlensing. Image credit: 

Originally posted on Forbes!

Every object in the universe with mass has the potential to bend light a little; the harder part is being able to measure that change.

This behavior of light, taking apparently curved paths around very massive objects, was one of the earliest tests of General Relativity. General Relativity suggested that all light should travel in locally straight lines, but if space itself was being warped due to the presence of massive objects, then the direction a beam of light might find to be “straight” might not look so straight to an external observer.

In this image the light from a distant galaxy, nearly 10 billion light-years away, has been warped into a nearly 90-degree arc of light in the galaxy cluster RCS2 032727-132623. The galaxy cluster lies 5 billion light-years away.Image credit: NASA; ESA; J. Rigby (NASA Goddard Space Flight Center); and K. Sharon (Kavli Institute for Cosmological Physics, University of Chicago)

In this image the light from a distant galaxy, nearly 10 billion light-years away, has been warped into a nearly 90-degree arc of light in the galaxy cluster RCS2 032727-132623. The galaxy cluster lies 5 billion light-years away.Image credit: NASA; ESA; J. Rigby (NASA Goddard Space Flight Center); and K. Sharon (Kavli Institute for Cosmological Physics, University of Chicago)

An extreme case of the deflection of light exists as gravitational lensing. Gravitational lensing occurs when you have two objects lined up, one behind the other, and the light from the more distant object winds up curling around the closer, massive object, like water from a tap flowing around your fist. As a result, you can get multiple images of the same object; instead of a single jet of water hitting the bottom of the sink, the water splits, and hits the sink in a few places. The way that the light flows around the heavier object tells you about the exact alignment of the two objects, but it also tells you in great detail about the concentration of mass for the object in front. You can imagine that if you ran water over your fist, it would create a different landing pattern than if you ran it over a bowl, and different again if you ran water over a wine glass.

Typically we hear about gravitational lensing from studies of distant galaxies, where we’re able to observe an extremely distant object in great detail because gravitational lensing spread the light out over a wider area of the sky, or because the gravitational lens magnified the light from the object, making it brighter and easier to spot. But these galaxies aren’t the only thing we can observe using these methods; smaller scale objects work just as well.

Still of an animation illustrating how gravitational microlensing works. On the left, a diagram of how the brightness changes as the foreground star moves from right to left across the background star. On the right is a top-down image of the light path, and in the middle, a simulated view from Earth. Image credit: NASA's Goddard Space Flight Center Conceptual Image Lab

Still of an animation illustrating how gravitational microlensing works. On the left, a diagram of how the brightness changes as the foreground star moves from right to left across the background star. On the right is a top-down image of the light path, and in the middle, a simulated view from Earth. Image credit: NASA's Goddard Space Flight Center Conceptual Image Lab

In fact, this is one of the ways that you can find exoplanets. Say you’re looking at two stars which happen to be lined up; the light from the more distant one will bend around the mass of the star in front. If you have planets orbiting that star, the mass of the planet can bend the light a little further than you might otherwise expect. If the planet is massive enough, and all is very perfectly aligned, this additional distortion can wind up producing an extra image of the background star. Because the effect is relatively small, this method works best if the two stars are very closely aligned, which also means it works best if your planet is also very close in to its parent star.

The tricky part is measuring it! All the nearby stars are measurably in motion, and so the alignments between any two stars are fleeting. On top of that, you need extremely well calibrated data to be able to catch these small changes to a star’s light, as it passes behind another star. One such survey, the Optical Gravitational Lensing Experiment (OGLE) has been running for 25 years, and while its main goal isn’t finding exoplanets, it’s found a few through gravitational lensing measurements anyways. However, an upcoming NASA mission, the Wide Field Infra-Red Survey Telescope (WFIRST) has the detection of exoplanets by microlensing events as one of its main science goals, so when it launches in the 2020s, we should expect to be inundated with new exoplanets all over again - they're expecting to find at least 2,000 new planets.

Have your own question? Feel free to ask! Or submit your questions via the sidebarFacebook, or twitter.

Sign up for the mailing list for updates & news straight to your inbox!

Are We Missing Intelligent Life Because We're Looking Into The Past?

Scientists around the world say that they have found new planets thousands, millions or billions of light years away from Earth. Doesn’t that mean that the images those scientist receive are thousands or millions or billions of light years old? If intelligent life formed in one of those planets, and if they are also searching for new planets, then doesn’t it mean that those life forms will see only a rocky planet not habitable to life?
This artist’s impression shows the super-Earth 55 Cancri e in front of its parent star. Using observations made with the NASA/ESA Hubble Space Telescope and new analytic software scientists were able to analyse the composition of its atmosphere. It was the first time this was possible for a super-Earth. 55 Cancri e is about 40 light-years away and orbits a star slightly smaller, cooler and less bright than our Sun. As the planet is so close to its parent star, one year lasts only 18 hours and temperatures on the surface are thought to reach around 2000 degrees Celsius. Image credit: ESA/Hubble, M. Kornmesser

This artist’s impression shows the super-Earth 55 Cancri e in front of its parent star. Using observations made with the NASA/ESA Hubble Space Telescope and new analytic software scientists were able to analyse the composition of its atmosphere. It was the first time this was possible for a super-Earth. 55 Cancri e is about 40 light-years away and orbits a star slightly smaller, cooler and less bright than our Sun. As the planet is so close to its parent star, one year lasts only 18 hours and temperatures on the surface are thought to reach around 2000 degrees Celsius. Image credit: ESA/Hubble, M. Kornmesser

Originally posted at Forbes!

The search for planets outside our solar system has been expanding pretty rapidly recently with the data coming back from the Kepler mission, but nobody has managed to detect a planet quite as far away as a billion light years from Earth. Kepler can only detect Earth-like planets that are less distant than 3000 light years away from our solar system, in a very narrow region of our galaxy.

Our galaxy is about 50,000 light years from center to edge (so about 100,000 light years across), and the next nearest large galaxy is Andromeda, sitting about two and a half million light years away from us. While our current observations of the Milky Way lead us to believe that there’s a planet around pretty much every star in our galaxy, we haven’t been able to survey that much of our own galaxy, let alone the stars in Andromeda, which would be exponentially more difficult to observe. The furthest solid detection of an exoplanet is still only about 21,000 light years away.

But you’re absolutely correct - our images of exoplanets are just as out of date as they are distant from us, and we won’t ever be able to get around that limitation unless we can go visiting them so that the light-delay isn't so severe. A planet that we see at 10,000 light years distant from us will be an image that has traveled for 10,000 years.

In this rare image taken on July 19, 2013, the wide-angle camera on NASA's Cassini spacecraft has captured Saturn's rings and our planet Earth and its moon in the same frame. It is only one footprint in a mosaic of 33 footprints covering the entire Saturn ring system (including Saturn itself). At each footprint, images were taken in different spectral filters for a total of 323 images: some were taken for scientific purposes and some to produce a natural color mosaic. This is the only wide-angle footprint that has the Earth-moon system in it. Image credit: NASA/JPL-Caltech/Space Science Institute

In this rare image taken on July 19, 2013, the wide-angle camera on NASA's Cassini spacecraft has captured Saturn's rings and our planet Earth and its moon in the same frame. It is only one footprint in a mosaic of 33 footprints covering the entire Saturn ring system (including Saturn itself). At each footprint, images were taken in different spectral filters for a total of 323 images: some were taken for scientific purposes and some to produce a natural color mosaic. This is the only wide-angle footprint that has the Earth-moon system in it. Image credit: NASA/JPL-Caltech/Space Science Institute

On a geological timescale, 10,000 years is just a blip of time - the Earth was pretty much in the same shape as it is now, though we humans had made fewer changes to its surface. On a human timescale, 10,000 years has made a big difference. 10,000 years puts us back into the Neolithic era - the end of the Stone Age, around the time when pottery was developing, and we were beginning to cultivate plants for agriculture. So an intelligent civilization, 10,000 light years distant, that is just now looking for other life in the Universe would spy our Earth as a rocky planet with an atmosphere, far enough away from our sun that water could exist in our atmosphere, and if they managed to examine our atmosphere, they would notice that it is mostly nitrogen, with some oxygen and carbon dioxide in it as well, and that it contains water vapor. They would not be able to tell that there are creatures on that planet that are 10,000 years away from developing the internet, neurosurgery, and machines able to detect tiny distortions in space itself.

This kind of time delay is one of the reasons that scientists get extra excited when they find a nearby rocky planet that might be able to have liquid water on its surface - if the planet is close to us, then the time delay isn’t as bad as a more distant planet. (It is also much easier to observe these nearby planets in any degree of detail - the farther away you are from the Earth, the harder these measurements get.) We only managed to detect the contents of the atmosphere of a slightly-bigger-than-Earth planet for the first time a few days ago — unfortunately that planet is totally devoid of water, having an atmosphere of mostly hydrogen and helium, with some hydrogen cyanide thrown in for extra poisonous flavor. This planet is only 60 light years away, so our image of it is only out of date as far as 1976— this particular planet won’t have evolved into a friendlier, life-hosting planet in such a short time.

But let’s say a super-intelligent civilization out there has built an impossibly large telescope, and has the power (and the time) to detect planets orbiting stars in a distant galaxy, and they pointed it at our Earth. If they happened to be 2.5 billion light years distant, our planet’s atmosphere would be in the middle of a dramatic change. 2.5 billion years ago, our planet was in the middle of the Oxygen Catastrophe - the earliest photosynthetic bacteria were dumping oxygen into the atmosphere faster than it could be absorbed, and oxygen was slowly building up. As oxygen was a toxic byproduct to the single-celled life which had been living in a delightfully oxygen-free environment, they would have to adapt or die off. Observations of our planet from that distance would be able only to tell the observer that our planet existed, it has water in its atmosphere, and how rapidly we travel around our star, but not so much as a hint to our space-exploring future.

Have your own question? Feel free to ask! Or submit your questions via the sidebarFacebook, or twitter.

Sign up for the mailing list for updates & news straight to your inbox!

Dear Astroquizzical - Why has the discovery of exoplanets only happened recently?

This artists’s cartoon view gives an impression of how common planets are around the stars in the Milky Way. The planets, their orbits and their host stars are all vastly magnified compared to their real separations. A six-year search that surveyed millions of stars using the microlensing technique concluded that planets around stars are the rule rather than the exception. The average number of planets per star is greater than one. Image credit: ESO/M. Kornmesser

This artists’s cartoon view gives an impression of how common planets are around the stars in the Milky Way. The planets, their orbits and their host stars are all vastly magnified compared to their real separations. A six-year search that surveyed millions of stars using the microlensing technique concluded that planets around stars are the rule rather than the exception. The average number of planets per star is greater than one. Image credit: ESO/M. Kornmesser

Originally posted at Forbes!

Exoplanets (planets orbiting a star other than our own) have been much more present in the public eye since the launch and tremendous success of the Kepler planet-hunting satellite, which was really very recent; Kepler was launched in 2009, and had a few solid years of observations of a single patch of the Milky Way. But that’s not to say that scientists weren’t looking for them before then; the first tentative discoveries that were later confirmed to be real exoplanets happened in the late 1980s.

These early discoveries were slow, painstaking measurements, and had to focus on individual stars for long stretches of time, to be sure that a planet was the best explanation for whatever signal you saw in the light.  What hashappened recently is that we’ve found a way to be much more efficient in our searching, so the number of known planets outside our solar system has skyrocketed.

To find an exoplanet, there a couple of different methods you can try, and in either case, the actual measurement that you need to take is reasonably straightforward in principle. In practice, as with many things where the Universe is involved, this will pretty rapidly get more complicated.

One of these methods is to look at the spectrum of the star you suspect has a planet.  There are characteristic absorption & emission features in the spectrum of light that we observe; if we notice motion of those absorption and emission features, then we can plot those shifts over time. If there is a planet, you expect the star to wobble a little bit, because the gravity of the planet will tug on the star a little bit, very slightly pulling it off center.  It’s this wobbling motion that you detect by watching the spectrum of the star itself.  However, you have to watch the star for a long enough time to watch the star wobble a few times, which means you have to be taking data on your star pretty regularly (once every few days, in all likelihood) in order to be sure that you’re catching any kind of orbiting planet that’s possible.  This method tends to be most effective at catching really massive planets, very close to their parent star, since they’re the ones that pull the most on your star, and the bigger the pull, the easier it is to measure that wobble.

Another common measurement is to just stare at the star with a very sensitive camera, and watch for changes in brightness.  If you have a change in brightness - maybe the star seems to dim by 10 percent - and if that change repeats itself regularly, then what you’re looking at is likely to be an object passing in front of the star, which produces less light than the star itself.  Doing this from the ground means that your camera has to be astonishingly well calibrated to be sure that any changes to the brightness of the star aren’t due to changes in the atmosphere, and even then, you’re most likely to find planets which are large and therefore block a lot of light.  (Note: large in this case doesn’t necessarily mean they also have to be particularly massive, though at least with planets they often go together.)  Again, this means taking regular measurements of individual, probably nearby stars, over a long period of time, so that you can catch the repeated flickering of the star’s light as it’s blocked.

If you want to avoid the atmosphere, then you have to put your telescope in space, which suddenly makes your planet hunting endeavor much more expensive.  But this is where the Kepler satellite comes back into the picture.  Kepler, orbiting the sun, avoids the Earth entirely, and points at a patch of sky away from the Sun.  Kepler has one of the most fantastically precise cameras attached to it, which is able to detect changes to the brightness of a star’s light to much greater detail than ever possible on the Earth.  Kepler can also monitor a huge number of stars at once; instead of focusing on an individual star, Kepler can monitor 100,000 stars at once.  Ground based telescopes are not really designed to do this - they’re meant as multi-purpose sky observers, whereas Kepler was designed exclusively to find these fluctuations; Kepler is much more a single-purpose device.

So to go back to your question, of why this has only picked up recently – this has been an ongoing project of the scientific community for many decades. It’s just that these measurements are remarkably difficult to make from the ground, and we only recently got a planet-hunting satellite to go observe a fraction of our galaxy for a while. Once we got a device that’s custom-built to hunt for planets, then we were able to - so far – identify over a thousand planets orbiting distant stars.


Have your own question? Feel free to ask! Or submit your questions via the sidebar, Facebook, twitter, or Google+.

Sign up for the mailing list for updates straight to your inbox!