Astronomers Figure Out How To Weigh Entire Planets Using Starlight

This seems like an interesting development in space science.

Although astronomers have figured out how to measure the mass of planets in our own solar system a long time ago, it's practically impossible to weigh exoplanets. Well, it was until recently.

MIT planetary scientists Julien de Wit and Sara Seager just devised a method that enables them to weigh an exoplanet by measuring the starlight that shines through its atmosphere. It's so simple, it's genius. See, when an exoplanet passes in front of its star, it causes a blip in the amount of light that shines toward Earth. This is actually how we're able to discover exoplanets in the first place.

Not all of the starlight zooms past the exoplanet, though. Some is actually filtered through the atmosphere, and by measuring the spectrum of that light, the MIT scientists are able to learn all kinds of things about the planet, such as atmospheric pressure, temperature, and gravitational pull. With that information, they've come up with a new method for calculating not just atmospheric chemistry but a planet's weight and mass.

The main reason that this discovery is significant, is because astronomers can now deduce whether a planet is gassy or rocky like Earth. It also makes it easier to discover new exoplanets which brings us that much closer to finding an Earth twin.

Story:
gizmodo.com...

reply to post by pandersway


do you mean gassy like jupiter and rocky like earth? venus is a rocky planet too

reply to post by NiZZiM


Yeah I found that also a bit confusing when I read this article. Perhaps they meant Jupiter. But does the fact remain: Can astronomers now determine this difference between gaseous vs rocky type surface?

Wouldn't you need to actually weigh a planet as a control before you can use the info to start making weight predictions of other planets. The percentage might be close when comparing things but the weight or mass could be extremely off. I don't know much about this but what I say seems logical to me.

reply to post by rickymouse


Yeah we can't actually weigh a planet but they can compare to known masses within our solar system and perhaps make judgements as to whether or not a planet is somewhat earth-like. This is just my idea...not a scientist or an astronomer.

reply to post by pandersway


They had a problem guessing the mass of the asteroid that hit Russia. The numbers kept getting revised higher. The size also increased from what was originally thought. Now that they have an actual chunk of that asteroid to analyze, they have a better idea. A planet is made up of a variety of elements with the crust being different than what is inside. To say that we can know the density of a planet is absurd. The most that can be done is to take a guess, which could be way off. The composition of the inside of a planet can vary, the overall diameter can be measured fairly accurately but the mass cannot be truly known. There is a lot we do not know about these things. Most of what we know is from observations of things happening, not actual scientific evidence. Now that they have ways of actually testing these things they are constantly finding that what they thought was real is actually not. The basis of our knowledge was formed by the ideas of our forefathers who had no way to test if it was right. They found evidence to back their assumptions. Now remember....these evidence backed assumptions were used to form modern testing guidelines and they may be flawed. I would guess that half of what we think of as real is not real. Occams Razor has cut the truth many times to satisfy consensus of other scientists. Cut the truth even a little and it is not the truth.

Oh well, that is the way it is in the world nowadays, I guess we have to learn to live with misconceptions even though we have the ability to clear them up.

reply to post by rickymouse


Agreed. Its nice that they are trying difefrent methods to get it right, however until we can test this more thoroughly I'd be more comfortable with calling this an educated guess.

I was expecting a light hearted humorous comment from you. But an intelligent post will have to do for now

This is intresting. You could probably get some rough estimates on what could be on the planet.

pandersway
reply to post by NiZZiM

 

Yeah I found that also a bit confusing when I read this article. Perhaps they meant Jupiter. But does the fact remain: Can astronomers now determine this difference between gaseous vs rocky type surface?

Yes. Because density can be calculated if you have both the mass of the planet derived from radial velocity (one planet finding method) and the depth of the transit lightcurve (another planet finding method) which gives us the planets radius as it passes between us and its star.

When we are lucky enough to have both radial velocity AND a planetary transit detection we can then calculate the planetary density to see if a planet is rocky, gaseous or a water world.

So until now we have needed to have two different kind of measurements from two very different types of observations of a planet's effect on its star to know what the planet was mostly made out of.


Why this new discovery is significant is because it means we only need transit data and do not need radial velocity data to determine whether a planet is rocky or gaseous or mostly water or ice.


I should also note that some of the larger exoplanets (gas giants) have had pictures directly taken of them so we know their mass and radius and thus density the same way we know Jupiter's.

Is it just me or are the majority of methods of finding, measuring, figuring out composition etc, of planets, cannot be proven? yet most people take these THEORIES as FACT, because they say it is so.


With that being said, i think it is fascinating what theories they can come up with. If it is true it is pretty awesome, however, until someone lands on one of these planets that they have found, measured its size and composition, and proven it I will hold it as just that, a Theory

smithas05
Is it just me or are the majority of methods of finding, measuring, figuring out composition etc, of planets, cannot be proven? yet most people take these THEORIES as FACT, because they say it is so.



With that being said, i think it is fascinating what theories they can come up with. If it is true it is pretty awesome, however, until someone lands on one of these planets that they have found, measured its size and composition, and proven it I will hold it as just that, a Theory

Without getting into the the the scientific definition of theory (which is discussed ad nauseum on ATS because many people such as yourself misunderstand the word in a science context)....

Exoplanets are NOT theoretical objects. They have been measured and observed using time tested techniques which we've used for decades or even hundreds of years in our own solar system.

Using mass and radii to deduce what a planet is made out of is pretty well established, it's worked well for the planets in our solar system.

This stuff is based on complicated but very solid mathematics and things like Kepler's Laws of Motion.

Before we could send probes to the outer planets for example, we knew the density of them which gave us some idea into what they were made out of strictly based on similar measurements. The probes we sent in the 60s, 70s and 80s underscored what the math was telling us all along.

Never underestimate math.

The search for exoplanets is a very interesting and exciting one. I have seen many commentaries that have latched onto the discovery of super Jupiter's orbiting extremely close to their host star in order to say "oh astronomers don't know anything, they are all wrong, What do they know? Ha Ha Ha" and the such

But when you understand how these techniques work, you understand that they first started to see the easy stuff... the easiest stuff being where you look at a star and watch for it to be orbiting apparently in a two or more body system. How? Well when a star is in a two body system it the system does not have to have a centre of mass at the centre of the host star, it can be slightly off centre. thus the star itself swings around a little bit. You can look at the slight doppler shift this has on its atmosphere and infer if there is a large object orbiting it. This is why searches have found a lot of interesting objects and found lots and lots of brown dwarf binaries.

Transit method is also extremely important, but much more difficult, and relies on a number of developments that have come about in recent years. That is the ability to watch a star and measure its flux and watch it over a time scale of minutes to hours in time scale. Previously, this was not possible due to slow processing times for plate film, and then CCDs which sometimes can require hours of exposure.

You look for the slight dip in light from a host star, and here is the beauty. When you look at a star, you can from its spectra tell how hot the photosphere is. Knowing the spectral type -> temperature, and apparent brightness, it is possible to infer the diameter of the object. So with an approximate diameter and spectral flux. Watching for a small Earth sized object to pass in front, It will be done and gone in a matter of minutes/hours. So highspeed CCDs are required, and not only that but spectroscopes. You then watch for the spectral lines to be different when during these events.

this has actually been done many times before, though its likely the researchers at MIT took a batch of other data and plotted a few things together and found a good theoretical basis for a size/spectra relationship.


Its funny how many of the posts here have resorted to the "I dont believe it until X Y and Z happens." People here talk like scientists pluck these things from their butt. While people like those on ATS (Not mentioning any names" Sit there drooling about the wording of some of these things, and generally saying "We don't know anything because basically i dont understand it, so these scientists are obviously liars and making lots of money" talking about semantics and spend hours and hours going through things that are extremely simple for the sake of an argument which boils down to a rhetorical question.

It is very good to question and think about things, but please please please, Think before making stupid throw away comments. No we have not been to an Exoplanet, but we are collecting alot of good evidence that they exist, and we are trying to understand the universe. What more do you want? We are currently doing more than most, who to be fair, hardly even notice the universe exists outside of their narrow window... oh but that narrow window is best right because at the end of the day, these boffins haven't "been there" so ner ner ner nerrrr.

Rant aside...Amazing work!!!!

Some of the more weird ones are when finding White dwarfs or neutron stars with a few planets... very very weird objects

Thank you so much for your reply Eros. It was sorely needed. I'm new here and I have had to walk a delicate line to avoid offending some people.

Now I wonder if you can drop in the thread about Quantum Computing to explain why it is impossible to send information via quantum entablement faster than the speed of light?

I've tried but I think I am tripping over my shoes since this is way outside the scope of my studies, but right in your wheelhouse.

reply to post by JadeStar


Wow you explained it quite eloquently thanks.
Perhaps its all the layman's terms you used.
Us laymen dont like new things and big words

But seriously nice job explaining this.