Astronomy - 06.2019

ASTRONEWS

Comet 67P/

Churyumov-Gerasimenko

Asteroid 216

Kleopatra

Asteroid 624

Hektor

Comet 1P/Halley

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Although we imagine that Earth’s oceans make

it a watery planet, our home is actually only a

tiny fraction of water by mass. And in other plan-

etary systems, water is more common than our

own planet implies: Some exoplanets are up to

50 percent water by mass. So, what causes some

planetary systems to stay wet, while others dry

out? The answer might be aluminum, says a

Nature Astronomy study published February 11.

Lead author Tim Lichtenberg of the University

of Oxford told Astronomy that when large

amounts of aluminum-26 — a radioactive form

of aluminum — decay, the process can heat up

and dry out the large boulders that collide to

form planets. As a result, the amount of alumi-

num in a young star system could predict which

types of planets will evolve there.

Aluminum heating matters only for bodies

of a certain size. Small pebbles don’t have

enough aluminum-26 to cause any heating.

Full-size planets may be able to retain their

water through other methods, such as in an

atmosphere. But aluminum heating would

affect all objects in the unlucky size range

between 5 and 50 miles (8 and 80 kilometers).

A good example of this effect in action

might be the TRAPPIST-1 exoplanet system,

which appears unexpectedly dry. However,

Lichtenberg points out there’s no solid proof

that aluminum heating caused either our solar

system’s or TRAPPIST-1’s relative dryness, so

this new idea remains just one possibility out of

potentially many. “This is not the only method”

that can dry out systems like TRAPPIST-1, he

said. “But it is a powerful one.” — K.H.

Think that Earth’s atmosphere only encompasses,

well, Earth? Think again. New findings published

February 15 in the Journal of Geophysical Research:

Space Physics show that our atmosphere stretches

much farther into space than previously thought.

Researchers made this discovery while “dusting

off” data from ESA/NASA’s Solar and Heliospheric

Observatory (SOHO), which has been studying the

Sun since 1995. Between 1996 and 1998, the space-

craft used its sensors to trace Earth’s geocorona —

the cloud of hydrogen atoms appearing where

Earth’s atmosphere meets outer space. When these

atoms interact with the Sun, they emit ultraviolet

light, visible in this image taken by Apollo 16

astronauts on the Moon in 1972.

SOHO used this light to measure how far the

geocorona extends. To their surprise, the researchers

found that the Moon, which sits about 239,000 miles

(385,000 kilometers) from Earth, lies well within the

geocorona’s boundary, which stretches 390,000 miles

(630,000 km) into space. Now, the team hopes to

use this technique to detect hydrogen in the

atmospheres of more distant planets. — A.J.

Radioactivity may dry out water worlds

Earth’s extended atmosphere

The amount of data in the Pan-STARRS

digital sky survey’s second release.

It is the largest amount of

astronomical data ever published,

equivalent to 2 billion selfies.

1.

PETABYTES

HEAT IT UP. This artist’s concept illustrates how a planet’s birthplace affects the amount of radioactive aluminum

it inherits. At left, a planet formed in a massive, dense star cluster is subject to significant bombardment, resulting

in a hotter, drier planet. The world at right, formed in a different environment, receives less aluminum-26 and stays

cooler and wetter. THIBAUT ROGER

MEET SOME CONTACT BINARIES

ODD COUPLE. In

January, New Horizons

flew by the Kuiper Belt

object Ultima Thule (MU 69 )

and identified it as a

contact binary: a double-

lobed object made up of

two bodies that have

come together until they

are gently touching. This

odd arrangement is not

unique in our solar system;

there are numerous other

bodies that astronomers

believe are contact

binaries, many of which

are closer to home in the

main asteroid belt or

circling the Sun as short-

period comets. Here are a

few of the solar system’s

more famous contact

binaries. — A.K.

HIDDEN FIGURE. NASA has renamed its Independent Verification and Validation Facility, which ensures the

agency’s missions succeed by confirming their software performs correctly, in honor of Katherine Johnson.

As of July 2018, astronomers had

identified 83 suspected contact

binaries in our solar system: 69

asteroids, eight trans-Neptunian

objects, and six comets.

FAST

FAC T

ASTRONOMY

: ROEN KELLY

NASA