BBC Knowledge June 2017

STAR

Mercury

Mars

4

2

1

1b

1c

1d

1e

1f

1g

Venus

Earth

1h

HOT AND COLD

Orbital period Days

Distance to starAstronomical units (AU)*

Planet radiusRelative to Earth

Planet massRelative to Earth

1.51

0. 011
   1.09
   0.85

b c e f g h

2.42

0.015

1.06

1.38

d

4.05

0.021

0.77

0.41

6.10

0.028

0.92

0.62

9.21

0.037

1.04

0.68

12.35

0.045

1.13

1.34

~20

~0.06

0.76

TR APPIST-1

solar system

TRAPPIST-1

solar system

Our Solar

System

4

8

This illustration compares the energy received by TRAPPIST-1’s planets, relative to Earth. TRAPPIST-1’s planets are named 1b-1h.
It is thought that 1b, 1c and 1d are probably too hot to support liquid water, and 1h is too cold. But the other three could host oceans –
and, therefore, life.

* 1 AU = distance from Earth to Sun

Asteroid belt

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