Astronomy - 06.2019

ASTRONEWS

5°

DORADO

PUPPIS

CARINA

VOLANS

RETICULUM

LMC

Canopus

South Celestial Pole

WWW.ASTRONOMY.COM 13

For the first time ever, astronomers think

they’ve discovered an exoplanet that

survived a catastrophic collision with another

planet. The evidence for the impact comes

from two “twin” exoplanets that seem a

bit more fraternal than identical, accord-

ing to research published February 4 in the

journal Nature Astronomy.

The pair of planets in question (along with

at least two other planets) orbit a Sun-like star

in the Kepler-107 system, roughly 1,700 light-

years away in the constellation Cygnus the

Swan. Known as Kepler-107b and Kepler-107c,

these planets have nearly identical sizes (both

have a radius of roughly 1.5 times that of

Earth), but the inner planet, Kepler-107b, is just

one-third the density of Kepler-107c, which is

more than twice as dense as Earth.

Previous studies have shown that intense

stellar radiation can strip the atmosphere from

a planet that sits too near its host star. But if

the inner planet lost its lighter atmospheric

elements, it should be denser than its twin,

not less dense. According to the paper, this

would “make the more-irradiated and less-

massive planet Kepler-107b denser than

Kepler-107c,” which is not the case.

However, there is another way that a planet

can lose a lot of mass: by getting whacked by

another planet. This is exactly what the

researchers think happened to Kepler-107c.

The team argues that the denser planet,

Kepler-107c, likely experienced a massive colli-

sion with a third, unknown planet at some

point in its past. Such a gigantic impact, the

study says, would have stripped the lighter sil-

icate mantle from Kepler-107c, leaving behind

an extremely dense, iron-rich core. According

to the study, Kepler-107c could be as much as

70 percent iron.

Though further research is needed to con-

firm the hypothesis, if proven correct, this find

would become the first evidence for a plane-

tary collision outside our solar system. — J.P.

First evidence of exoplanet collision

DOUBLE DOWN. A NASA researcher found a 23-mile-wide (37 kilometers) impact crater beneath the Greenland ice.

The new crater is about 100 miles (160 km) from a 19-mile-wide (30 km) crater discovered just three months before.

Though it originally appeared as a snowman

made up of two globes, the Kuiper Belt object

Ultima Thule is actually more of a pancake.

The new view comes from parting shots taken

with the Long-Range Reconnaissance Imager

on NASA’s New Horizons on January 1, as the

spacecraft was already 5,494 miles (8,862 kilo-

meters) past the contact binary. Researchers

reconstructed the object’s shape by watch-

ing background stars disappear behind it in

separate images, revealing that the larger

lobe, Ultima, is flattened like a pancake while

the smaller lobe, Thule, is shaped more like a

dented walnut, according to a press release.

Going back over previous data, researchers

confirmed that their new model of Ultima

Thule’s shape is consistent with the character-

istics gleaned from all prior observations. “We

had an impression of Ultima Thule based on

the limited number of images returned in the

days around the flyby, but seeing more data

has significantly changed our view,” said New

Horizons principal investigator Alan Stern.

The object’s true shape has left researchers

wondering about its formation, but will cer-

tainly shed further light on the processes that

shaped our outer solar system. — A.K.

Ultima Thule reveals

its flatter shape

INCOMING! A planetary collision is exactly as bad as you would imagine. Unlike an asteroid impact, there’s not

just a crater left behind. Instead, such a massive crash strips the surviving world of much of its lighter elements,

leaving behind the dense core. NASA/JPL-CALTECH

ABOVE JUPITER’S THICK ATMOSPHERE

A FISHY SCENE. If you stood on the

cloud tops at the south pole of Jupiter and

looked straight overhead, these are the

stars you would see. The gas giant’s axis

points toward a nondescript region

in the constellation Dorado the

Dolphinfish, some 12° away from

the night sky’s second-brightest

star, magnitude –0.7 Canopus.

Even more impressive, the

center of the Milky Way’s

galactic neighbor, the Large

Magellanic Cloud (LMC),

sits just 5° away.

— Richard Talcott

FAST

FAC T

Because Jupiter’s Galilean

moons orbit in the planet’s

equatorial plane and their axes

are perpendicular to their orbits,

observers at their south poles

would have similar views.

STRANGE SHAPE. The top image of Ultima

Thule averages 10 separate frames; the image

below it has been processed to eliminate

blurring due to motion. NASA/JHUAPL/SWRI/NOAO

ASTRONOMY

: ROEN KELLY