Astronomy - USA (2020-08)

8 %

Other

< 0.1%

Other

0.7%

Other

MERCURY VENUS EARTH MARS

42 %

Oxygen

22 %^

Sodium

22 %

Hydrogen

0.9%

Argon

6 %

Helium

96 %

Carbon dioxide

4 %

Nitrogen

78 %^

Nitrogen

21 %^

Oxygen

95 %

Carbon dioxide

2.7%

Nitrogen

1.6%

Argon

0.1%

Other

(carbon dioxide,

water, etc.)

2010 2011 2012 2013

The Sun

Year

2010 2011 2012 2013

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Year

KIC 7849521

12 ASTRONOMY • AUGUST 2020

QUANTUM GRAVITY

A BREATH OF FRESH AIR. Although the amount of each varies from one to the next, the

terrestrial planets in our solar system have atmospheres composed largely of the same few

elements, with others present in trace amounts. Astronomers believe these atmospheres are

not original to the planets, but are secondary atmospheres generated mostly through impacts

and outgassing. These graphs show the rough composition of the atmosphere of each planet

in our inner solar system, illustrating their similarities and their differences. — ALISON KLESMAN

FAST FACT

A column of air from

sea level to the top of

Earth’s atmosphere

with a base of 1 square

inch (6.5 square

centimeters)

weighs 14.7 pounds

(6.7 kilograms).

The Sun’s steady stream

of energy sustains life

on Earth. And, thank-

fully, that energy output

doesn’t usually fluctuate

enough to cause any

major problems. Mild

tantrums, in fact, even

produce the spectacles

we call aurorae. But

how does the Sun’s

behavior match up to

similar stars? A new

analysis of 369 Sun-like

stars, each with compa-

rable rotation periods

and other fundamental

features, shows our star

is extremely tame. And

based on radioactive

evidence trapped in

tree rings and ice cores,

it’s been like that for at

least 9,000 years. Data

obtained from 2009

to 2013 by the Kepler

Space Telescope indi-

cate that Sun-like stars,

such as KIC 7849521

(at left, bottom), exhibit

brightness fluctuations

averaging about five

times as strong as those

of the Sun. — JAKE PARKS

Our Sun is

strangely docile

TERRESTRIAL ATMOSPHERES

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