# TRAPPIST-1 now has seven planets. (Possible life?)

## 237 posts in this topic

29 minutes ago, justidutch said:

I am wondering if one or some of you can quickly outline what those parameters mean when they are describing the physical properties, as found here?  I know some of them are obvious, but most I don't really know what they mean, like a couple posts up @Shpaget is getting excited about ESI and I would like to know why!  Also the units of some of the units of the measurements, I'm not familiar with them (high school physics and math was >25 years ago…).  Thanks in advance!

Right ascension

Declination

Constellation

Apparent magnitudes

Parallax

Distance

Mass

Density

Effective temperature

Luminosity

Metallicity

Age

RA and declination are coordinates, they basically tell you where to look in the sky. So DMS units.

Constellation is the constellation in which the system appears from our planet. Not a measurement so no unit.

Apparent magnitudes are a log scale of luminosity of the star seen from Earth. The lower the apparent magnitude, the higher the luminosity. The letters stand for some standard astronomy filters which pick out different wavelengths of the spectrum. V is centred on visible, R on red, I J and K on different wavelengths in the infrared. Magnitudes are calculated using a log relation so they are dimensionless.

Parallax a measure of the distance using the angle formed by the orbit of the Earth, the Sun and the star itself. Using perspective from the further stars in the background you can measure the apparent displacement of the star and therefore the angle. High school trigonometry converts this into a distance. I suppose "mas" stands for milli-arcseconds.

Distance is the distance of the star to the Earth. Expressed in parsecs, a unit defined as the distance subtended by a 1° parallax, roughly 3.3ly.

Mass is the mass of the star. Expressed in solar masses* (ratio to the mass of the Sun).

Density is the mass density of the star. Expressed in solar densities* (ratio to the density of the Sun).

Effective temperature is the temperature derived from the light spectrum of the star (stars are pretty decent blackbodies so they have a specific temperature associated with their light spectrum). Unit is the Kelvin (the true and only way to express temperatures).

Luminosity is the luminosity (ie brightness) of the star. Expressed in solar luminosities* (ratio to the luminosity of the Sun).

Metallicity, here, is the ratio of iron to hydrogen masses in the star. Ratio so no units.

Age is the age of the star. Myr stands for Mega-year, or millions of years.

* When you see a symbol with a dotted circle as subscript, it's relative to the Sun. If it's a crossed circle, it's relative to the Earth. You also can sometimes see subscript J, that is Jovian masses (usually used for gas giants).

ESI is the Earth Similarity Index, a measure on how "close" an exoplanet is to the Earth, using its physical characteristics. IIRC it takes into account: mass, radius, surface gravity, equilibrium temperature and maybe other stuff.

Edited by Gaarst
Corrected some typos and added a few things.
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25 minutes ago, justidutch said:

I am wondering if one or some of you can quickly outline what those parameters mean when they are describing the physical properties, as found here?  I know some of them are obvious, but most I don't really know what they mean, like a couple posts up @Shpaget is getting excited about ESI and I would like to know why!  Also the units of some of the units of the measurements, I'm not familiar with them (high school physics and math was >25 years ago…).  Thanks in advance!

Right ascension

Declination

Constellation

Apparent magnitudes

Parallax

Distance

Mass

Density

Effective temperature

Luminosity

Metallicity

Age

EDIT: Ninga'd by @Gaarst

Alright, I'll take a crack at this, ESI is Earth similarity index, and goes from 0.0 (Not even remotely Earthlike) to 1.0 (An exact twin, or as close as you can get to one), TRAPPIST-1d has an ESI of 0.9 or 90% on the scale.

Right Ascension (Taken from google): The distance of a point east of the First Point of Aries, measured along the celestial equator and expressed in hours, minutes, and seconds.

Declination (Also from google): The angular distance of a point north or south of the celestial equator.

Constellation: A group of stars that make a pattern in the sky, like the Big Dipper.

Apparent magnitudes (From good ol' wiki): The apparent magnitude of a celestial object a number that is a measure of its brightness as seen by an observer on Earth. The brighter an object appears, the lower its magnitude value (i.e. inverse relation). The Sun, at apparent magnitude of −27, is the brightest object in the sky.

Parallax (Google): Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines.

Distance: Pretty straightforward, for light years, it's 5.878625 trillion miles. For Parsecs, it's 19.173511577 trillion miles.

Mass: The mass of an object in Astronomy is usually comparing one body with the Earth, Jupiter, or the Sun, depending on how massive it is, the same is for Radius, comparing the radius of a planet or star compared to the Earth, Jupiter, or the Sun.

Density (From google): The term density appears in astronomy in many different contexts. In its most generic use the density is the mass per unit volume of an object or region and might have units like kg/m^3 or Mo/pc^3.

Effective temperature (Google): the temperature of an object calculated from the radiation it emits, assuming black-body behavior.

Luminosity (From wiki): In astronomy, luminosity is the total amount of energy emitted by a star, galaxy, or other astronomical object per unit time.[1] It is related to the brightness, which is the luminosity of an object in a given spectral region.

Metallicity (From google): In astronomy and physical cosmology, the metallicity or Z is the fraction of mass of a star or other kind of astronomical object that is not in hydrogen (X) or helium (Y).

Age: How old an object is, I believe in astronomy, they measure the age by millions or billions of years.

Edited by Spaceception
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LIVESTREAM!

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7 hours ago, Nibb31 said:

How would that help ?

Just in terms of reliability and failure probability. With all the effort already provided, JWST must reach its L2 halo orbit in full operational condition.

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Since the planets experience tides with each other, could that mean their cores are hot and liquidy, and as such, could have strong magnetospheres?

Edited by Spaceception
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30 minutes ago, Spaceception said:

Since the planets experience tides with each other, could that mean their cores are hot and liquidy, and as such, could have strong magnetospheres?

Possibly. What's good is that based on its density, it can be predicted that TRAPPIST-1d is about 30-35% iron. A larger core can help lead to a larger magnetosphere.

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Just now, ProtoJeb21 said:

Possibly. What's good is that based on its density, it can be predicted that TRAPPIST-1d is about 30-35% iron. A larger core can help lead to a larger magnetosphere.

Woah. That is really good. What're their gravities?

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1 minute ago, Spaceception said:

Woah. That is really good. What're their gravities?

Here. g = GM/r2, have fun

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@Gaarst So I did it for all the potentially habitable planets

Trappist 1d: .687g

Trappist 1e: .73g

Trappist 1f: .614g

And Trappist 1g; 1.065g

Edited by Spaceception
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1 minute ago, Spaceception said:

So I did it for all the potentially habitable planets

Trappist 1d: .687g

Trappist 1e: .73g

Trappist 1f: .614g

And Trappist 1g; 1.065g

1b (Theros) has 0.717g

1c (Auxo) has 1.2282g

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3 minutes ago, ProtoJeb21 said:

1b (Theros) has 0.717g

1c (Auxo) has 1.2282g

So Auxo is the big boy of the bunch.

Edited by Spaceception
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12 minutes ago, Spaceception said:

And Trappist 1g; 1.065g

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Just now, max_creative said:

Yeah, you wouldn't feel that much heavier, it'd be like having a lightweight backpack on you, only without the bulkiness.

Although, I really want to visit T-1d

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On the subject of magnetic fields, although the planets will be tidally locked, their years are all very short, from 1.5 to 12 days for b to g. That means they will still actually be rotating relatively quickly. They will also be experiencing significant tidal heating, as well as having plenty of residual heat of formation left over due to being significantly larger than bodies like Mars. I see no reason why the inner planets especially wouldn't have reasonably strong magnetic fields.

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2 hours ago, regex said:

How many of these planets are face-locked to the star? I would be very interested in how that affects habitability and I really hope TRAPPIST-1 gives us an opportunity to study that.

I'm not sure it's possible to check if they are or not. They could run a simulation I guess, but even then we don't know how the mass is distributed throughout the planets' interior. If I'm not mistaken the Moon is tidally locked mainly because its core isn't directly in the center.

Unless we know all these things and someone could enlighten me. I would also like to know and I'm not an expert.

Edited by Veeltch

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I think with tidally locked planets there is a small sliver near the terminater that could be habitable if I am not mistaken.

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3 hours ago, Shpaget said:

Not even the Earth has that!!!

Yeah! It has 1.0!

2 hours ago, justidutch said:

Hmmm, I wonder how they calculate ESI accurately.  Do they go there and count the number of lawyers and telephone-box repairmen?

Nah, that would be Idiot Similarity Index (of which Earth has the highest)

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Amazing! We could (possibly) be standing on the threshold of a new discovery that will change the world forever, and shape the future of humanity! Its unlikely, but we need to have hope. I say we get arecibo to send a message! (Not that it would be helpful)

Edited by Emperor of the Titan Squid

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How long would it take to get there? I've seen varied estimates (all in the thousands of years). One article used New Horizon as the example of our fastest space craft and put its speed at 32,000mph and then estimated ~320,000 years, but I think it would be much longer than that, more like 820,000 years.

Also, these guesstimates are working of Trappist-1 being 39-40 light years away and calculating based on that distance. but I assume that's the direct (straight line) distance, and doesn't factor in orbital motion.  Which leads me to the next question; how do you transfer between solar systems?  Is it just like a scaled up version of planetary transfers, but taking the centre of the galaxy as the central point and then doing hohmann-ish transfers between solar systems based on that? If so that could add much much more time to the journey, never mind waiting for a transfer window.

and of course this all leads into wondering, what would the deltaV requirements be for such a mission? Lets say if we just wanted to send something small, like a Mk1-2 command pod and nothing else, how much dV would that take? I dread to think!

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51 minutes ago, Emperor of the Titan Squid said:

Amazing! We could (possibly) be standing on the threshold of a new discovery that will change the world forever, and shape the future of humanity! Its unlikely, but we need to have hope. I say we get arecibo to send a message! (Not that it would be helpful)

We have found a bunch of earth sized rocks whizzing around a small star. That's about all we know. Do we know if any atmospheres are present?

Edited by munlander1
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29 minutes ago, katateochi said:

How long would it take to get there? I've seen varied estimates (all in the thousands of years). One article used New Horizon as the example of our fastest space craft and put its speed at 32,000mph and then estimated ~320,000 years, but I think it would be much longer than that, more like 820,000 years.

Also, these guesstimates are working of Trappist-1 being 39-40 light years away and calculating based on that distance. but I assume that's the direct (straight line) distance, and doesn't factor in orbital motion.  Which leads me to the next question; how do you transfer between solar systems?  Is it just like a scaled up version of planetary transfers, but taking the centre of the galaxy as the central point and then doing hohmann-ish transfers between solar systems based on that? If so that could add much much more time to the journey, never mind waiting for a transfer window.

and of course this all leads into wondering, what would the deltaV requirements be for such a mission? Lets say if we just wanted to send something small, like a Mk1-2 command pod and nothing else, how much dV would that take? I dread to think!

You don't account for galactic orbit when transferring to stars. The Sun's galactic period is about 200 million years and it orbits at a few hundred km/s. Since the orbital are so big, the relative motions are small, and since the orbital velocity is very low for whatever would want to reach a star in a reasonable time, you can consider you're travelling in a straight line.

Waiting for a transfer would take about one synodic period of the star you want to go to with the Sun. Very long orbit + very close orbits (relative to the size of the Milky Way) = gigantic synodic period. Putting in numbers, the smallest synodic period for the Sun and TRAPPIST-1 is 113 billion years (that's 8 times the age of the Universe). A Hohmann transfer would take roughly half an orbital period, or 125 million years.

As for the dV, it depends on the time you want to wait to get there. Technically, escaping the Sun's attraction would be enough, so any rocket big enough to send a pod to Jupiter could do the job.
Since we're considering straight lines, the dV is basically the maximal speed you want to reach for your trip (twice if you want to stop there).

Edited by Gaarst
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TRAPPIST-1 system would be a very kerbal solar system. With such short distances between the planets traveling from one planet to the next would be as easy as us going to the moon, it is just the trips would be one way until a big enough rocket could be made to take off from one planet, land on the next and fly all the way back. So for any inhabitants living there could have a solar empire.

Edited by RuBisCO
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I wonder about how stabil their orbits are. They have gravity of between 0.5earth to 1.0earth while distance between two neighbor planets falls less than 600.000 km when their orbits' closest aproach happens. Very strong gravity, very short orbits, very weak Star.. could one planet throw other one to the some different orbit? AFAIK distance between Earth-Moon is something like 384.000 km

They are really close

Edited by oguz
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9 hours ago, munlander1 said:

We have found a bunch of earth sized rocks whizzing around a small star. That's about all we know. Do we know if any atmospheres are present?

Exactly, 3 of the planets seem to pass in front of the star. So for these there is a chance to get a spectrum of a possible atmosphere when the star's light passes through. If that is the case, i am sure that  someone will soon(tm) obtain such spectra, maybe after the discovery has been verified.

6 of the planets are assumed not to have formed in situ but farther out and migrated inwards. So they were not always under the conditions they are assumed to be now.

Edited by Green Baron

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11 hours ago, munlander1 said:

I think with tidally locked planets there is a small sliver near the terminater that could be habitable if I am not mistaken.

Not so bad, you are likely to get cloud cover over the equator part, if orbit is not totally circular you would also get wobble who would move the sun forward and back making light on more of the planet.
You would want plenty of water and an pretty thick atmosphere, with an dry planet its an huge risk the water end up on the backside.

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