How it works

What the chart is. It is drawn from NASA’s Exoplanet Archive as it stood on 11 November 2026. The archive listed 6,464 confirmed planets that day. The chart shows the 6,063 that have both a width and a length of year. Some of the widths were not measured directly: where only a planet’s mass is known, the archive works out a likely width from it.

Both scales are stretched so that each step is ten times the one before. Without that, nearly every dot would be squashed into one corner.

Kind	What NASA means by it
Gas giant	As big as Saturn or Jupiter, or much bigger. Mostly hydrogen and helium
Neptune-like	About the size of Neptune or Uranus
Super-Earth	Bigger than the Earth and smaller than Neptune, up to about 10 times the Earth’s mass. The name is about size only. It does not mean the planet is like the Earth
Terrestrial	The size of the Earth or smaller

The counts in this lesson were made for it from the archive’s table on the same day. They are not NASA’s own. Of the 6,063 planets on the chart, 5,019 have a year shorter than 88 days. Counting a hot Jupiter as anything more than 8 times as wide as the Earth with a year under 10 days gives 768. Counting everything from 1.25 to 4 times the Earth’s width gives 3,294, which is 54 per cent. Draw the lines somewhere else and the numbers change, but the picture does not.

Why the chart is lopsided. Three quarters of these planets were found by watching for a star to dim as a planet crosses in front of it, and most of the rest by the wobble a planet gives its star. Both ways favour big planets on tight orbits. A planet with a ten-year orbit has to be watched for ten years just to see it come round once. So the empty right-hand side of the chart mostly shows what has not been looked for long enough yet.

The first hot Jupiter was 51 Pegasi b, about 50 light years away, found in 1995. It was the first planet found round a star like the Sun. Some hot Jupiters go round in as little as 18 hours. One idea is that they form far out, where there is ice to build with, and drift inward while the star still has its disc of gas. Another is that the pull of other planets throws them in later. Both may happen.

A gap in the sizes. Planets between about 1.5 and 2 times the width of the Earth are rarer than those a little smaller or a little larger. It was found in the data from the Kepler space telescope and is sometimes called the radius valley.

55 Cancri e. The hottest part of its day side is at nearly 2,700 kelvin (about 2,400 °C) and the night side at about 1,400 kelvin, from 80 hours of watching by the Spitzer Space Telescope. Flowing lava is one explanation that has been offered for the way its heat is spread. Nobody has seen its surface.

The picture of a planet forming. The star is PDS 70. The planet, PDS 70b, is about 3 billion km from it, roughly as far as Uranus is from the Sun, and is at about 1,000 °C. The picture was taken in infrared light by the SPHERE instrument on the Very Large Telescope in Chile and published in 2018. It was the first clear picture of a planet caught while still forming.