Question 1

How near is the nearest?

Accepted Answer

About four light years — a planet around Proxima Centauri, the closest star to the Sun. On the scale of the galaxy that is next door, and on any human scale it is unreachable: no spacecraft yet built would arrive inside a hundred human lifetimes.

Question 2

Why are the nearest ones so useful?

Accepted Answer

Because they are the only ones a telescope has any chance of studying in detail. Starlight filtered through an atmosphere is a faint signal, and it falls off with distance like everything else, so the nearby systems are where the next decade of work will be done.

Question 3

How is the distance measured?

Accepted Answer

By parallax where the object is near enough — the shift in its apparent position as the Earth crosses its orbit, which is geometry and needs no assumptions. Beyond that, distance is inferred from how bright something of known luminosity appears, and the further out the ladder goes the more the uncertainty grows.

Question 4

How firm is the order?

Accepted Answer

Firmer at the top than at the bottom. Neighbouring rows often sit inside each other's error bars, so a swap between two adjacent entries is a revision rather than a correction. Each object's own page carries the figure with its uncertainty and the method it came from.

Question 5

Why are some exoplanets missing?

Accepted Answer

Because this catalogue holds no distance for them. A row with an empty distance column cannot be ranked on it, so the list is the nearest of those measured rather than the nearest that exist.

Question 6

Could we see one directly?

Accepted Answer

A handful of young, massive planets on wide orbits have been imaged directly. A rocky planet close to its star has not: it is some ten billion times fainter than the star and separated from it by a fraction of an arcsecond, which is a contrast no existing telescope can reach.

Question 7

Are any of them habitable?

Accepted Answer

Several sit at a distance from their star where liquid water could exist, which is the only thing that phrase means here. Whether any has water, an atmosphere or a surface is unknown, and around a flaring red dwarf the odds are worse than the distance suggests.

Question 8

Does every nearby star have planets?

Accepted Answer

Most appear to. Statistically there is at least one planet per star in the galaxy, and small planets are commoner than large ones — but a system without a favourable geometry or a large enough tug is undetectable with present methods, so absence from this catalogue is not absence of planets.

The nearest exoplanets to Earth

COMMON QUESTIONS