# Tag Info

53

To add to Rob's answer, I wanted to expand on where this naming convention comes from. The International Astronomical Union (IAU) is the organization which generally sets conventions and definitions. They're the ones who demoted Pluto to being a dwarf planet in 2006. Anyway, before any exoplanets were found, there existed a convention for naming multiple-...

40

The convention for planetary naming is that the closest planet to the star (if multiple planets are found at the same time) is named "star"b, then "star"c and so on. As correctly pointed out by Zephyr, if the discoveries are more haphazard, the order of discovery takes precedence over distance from the star). So, there is no Trappist-1a. Or you can think of ...

29

The star at the center of TRAPPIST-1 is called 2MASS J23062928-0502285. It was discovered by the Two Micron All-Sky Survey (2MASS), which imaged the whole sky in the infrared between 1997 and 2001. This resulted in a catalog of over 300 million objects. TRAPPIST-1 itself was cataloged in 1999. The name is actually its coordinates in right ascension and ...

22

Breaking the phrase down: Dwarf star - a term I will never understand - is used to describe relatively small, dim stars. Unfortunately, this encompasses most main-sequence stars, which are indeed dwarfs compared to large giants and supergiants. Ultra-cool, as called2voyage already discussed, means that the star has an effective temperatures of less than ...

19

No such planet has been announced as having been discovered. The paper only shows evidence for the 7 (really 6 because the 7th can't be officially confirmed with only 1 observation) terrestrial planets and does not make the case for any other planets. The paper doesn't indicate that more planets could exist, but does remark that there are large error bars on ...

18

Trappist-1 was first catalogued by the 2MASS survey about 17 years ago and has the catalogue number 2MASS J23062928-0502285. It was identified as an ultra- low-mass star with a spectral type of M7.5 by Gizis et al. (2000) and Cruz et al. (2003), using a combination of 2MASS and proper motion. The reason it was monitored by the Trappist telescope is that is ...

15

As BMF already pointed out, you won't really see any planets in such overview diagrams for TRAPPIST-1, either. At least not with more than a few pixels per planet. As I did not find a good model online, I would recommend looking at "Games" like Universe Sandbox or SpaceEngine. For the latter, older versions are even free. Then you can generate screenshots ...

10

We don't know. Much of what we do know - or at least think we know - about the planets' orbital parameters comes from simulations the team ran via $n$-body methods[1]. Some methods of integration led to short-term disruptions, on the order of less than $\sim10^6$ years. That said, the system is at least $5\times10^8$ years, and it would be odd if the ...

9

It's kind of hard to imagine distances on a solar-system scale. If the Earth was a basketball, for example, the Moon would be slightly smaller than a tennis ball and about 24 feet away. The Sun would be 80 feet across and nearly two miles away. The entire Trappist system, all seven planets, each of them thought to be larger than Mars, fits between the Sun ...

8

According to Spectroscopic Properties of Ultra-cool Dwarfs and Brown Dwarf by J.D. Kirkpatrick, the working definition of ultra-cool dwarf is: dwarfs having classifications of M7 or later. That is referring to the stellar classification system which categorizes stars by their spectral characteristics. Class M stars have a surface temperature less than ...

8

The luminosity of Trappist-1 is estimated to be $5.25\times 10^{-4}\ L_{\odot}$, but it has not always been like this. The luminosity of a brown dwarf decreases with time and it this measured luminosity (along with the spectral type) that allows an estimate of the mass and a lower limit to the age using stellar evolutionary models. If I look at the Baraffe ...

8

Using Wikipedia numbers, this is the TRAPPIST-1 dwarf star with companions b and c, distances and radii to scale. Here is a view of TRAPPIST-1b transiting its dwarf star, seen from low orbit around TRAPPIST-1c, with optical focal length 34 mm, and again distances and radii are to scale.

8

Are the planets in the TRAPPIST-1 system so close that inhabitants on one planet could see surface details on the other planets? Yes! How big would each planet appear from each of the other planets during conjunction or opposition? Bigger than Earth's moon? For some combinations, definitely! Here's a diagram of the size of each of the planets as seen from ...

6

I couldn't find one that respects the scale of the planets and their orbits, probably because the planets are just too small to be respected. I plotted the orbits of Trappist 1b-h, as well as Trappist 1 itself here in this image. Data for the orbits were taken from Wikipedia's page on the Trappist 1 planets. Surprisingly, each pixel represents about 10,000 ...

6

The probability of observing a planet transit is approximately $(R_p + R_s)/a$, where $R_p$ and $R_s$ are the planet and stellar radius respectively and $a$ is the semi-major axis of the planet's orbit. This assumes that planetary orbits are circular and randomly oriented with respect to our line of sight to the star (for which there is little or no counter-...

6

The dwarf star 2MASS J23062928-0502285 was first catalogued in 1999, if I've got that right. In May last year (2016) the Transiting Planets and Planetesimals Small Telescope–South (TRAPPIST) facility (its a .6 m automated scope in Chile) published their observations of the dwarf star and announced they had found 3 exo-planets orbiting it. Their ...

5

As the paper on the first three planets discovered around the star states, even though firm constraints have not yet been put on the masses of the planets, The results of planetary thermal evolution models — and the intense extreme ultraviolet (1−1,000 Å) emission of low-mass stars18 during their early lives — make it unlikely that such small planets ...

5

The reason is because exoplanets orbiting a star are named in the order they were discovered, starting with the letter b. Sometimes, in a system with two stars, say Alpha Centauri, there are two stars, Alpha Centauri A and Alpha Centauri B, no planes have been found in the system so far. If there were planets orbiting either one of those two stars, say for ...

5

This is a complicated question that would really require a full physics simulation and better knowledge of the system to accurately answer. But let's try a few back of the envelope calculations to see what we get. Calculating tidal forces from TRAPPIST-1c on TRAPPIST-1b I'm going to calculate the tidal effects of TRAPPIST-1c on TRAPPIST-1b (simply because, ...

5

The 2 big planets are probably f & g and they don't look up to scale to me. While f is the size of Earth, or almost 4 times bigger than the Moon, but it's also further away, ~ 1.3 million kilometers, as opposed to 400,000km for the Moon. So I would say f will be somewhat larger than the moon but not anywhere near what the poster shows. G will appear even ...

4

Hominids in the neighborhood is probably the biggest mistake made by the artist. Sorry to be a little less optimistic than people at NASA, but a journey this far would probably take hundreds of thousands of years. And we're not in the best condition to prepare for it. The technology needed for such a trip should take time to develop. Too much time, too ...

4

Using Kepler's laws. We can determine the orbital period, $P$, each planet has by just looking at the time between transits for a given planet. Each planet has a distinct transit so its easy to distinguish which planet is transiting and we can calculate a period pretty easily. Kepler's law then tells us that if you're orbiting with a specific period, you ...

3

As far as I know, and aside from direct communication, there's only one way to "find life" on another planet. That method is to look for molecular oxygen in the atmosphere. Molecular oxygen hates existing by itself and loves to combine with other atoms and molecules through oxidation. The Earth's atmosphere is currently ~30% $\mathrm{O_2}$, but that's only ...

3

The discovery, reported in the journal Nature, was made by astronomers using Nasa's exoplanet-hunting Spitzer Space Telescope. The telescope operates at the infrared wavelengths which glow brightest from TRAPPIST-1, and can detect the tiny dimming that occurs when a passing or "transiting" planet blocks out light from its star. Spitzer's data allowed the ...

3

That is a fascinating question due to the fact that planetary orbits have both absolute and relative spacing. The absolute spacing between planetary orbits is the number of kilometers that the semi major axis of the orbit of the outer planet exceeds the semi major axis of the orbit of the inner planet by. The relative spacing is the ratio between the semi-...

2

A website trappist.one has been created to detail information about this discovery. In the "Future" section, they specifically state: In the short term, photometric follow-up using the repurposed Kepler satellite (named K2) along with with newer observations using Spitzer ought to reveal the period of planet 1h. We will also search for additional ...

2

Another reason for the interest. Because the star is so dim and small, planetary signatures in the infrared stand out much better than they would with a sunlike star. The star has been described as an 'ultracool brown dwarf', which would imply that it doesn't have much nuclear fusion in its interior. The planets are incredibly close to their star (much ...

1

Let's take a look at the star and the planet's characteristics first. We have the star TRAPPIST-1: $M = 0.082 M_{\odot}$ $R = 0.117 R_{\odot}$ The planets are all roughly in the scale of $0.7 R_{\oplus}$ to $1.2 R_{\oplus}$ with their semi-major axes of: b: $1.66 \times 10^6 \; \mathrm{km}$ c: $2.88 \times 10^6 \; \mathrm{km}$ d: \$3.14 \times 10^6 \; \...

1

From this answer: Here's a diagram of the size of each of the planets as seen from each of the other planets. More details there. The scale is degrees, and for example the top row shows the largest possible size of planets c through h from planet b.

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