Astronomy

ASTRONEWS

Relative planet sizes are to scale, while distances are not.

Kepler-90 system

Kepler-90bKepler-90cKepler-90iKepler-90dKepler-90eKepler-90f

Kepler-90g

Solar system

Kepler-90h

FAST

FAC T

1

OSMIUM

22.61 g/cm^3

2

IRIDIUM

22.56 g/cm^3

3

PLATINUM

21.45 g/cm^3

4

RHENIUM

21.02 g/cm^3

5

GOLD

19.29 g/cm^3

10

MERCURY

13.55 g/cm^3

9

PROTACTINIUM

15.37 g/cm^3

8

TANTALUM

16.65 g/cm^3

6

TUNGSTEN

19.25 g/cm^3

7

URANIUM

18.95 g/cm^3

WWW.ASTRONOMY.COM 13

It’s official: The Sun is no longer the only star with

eight planets.

On December 14, NASA and Google held a joint

teleconference to announce the recent discovery of

an eighth planet orbiting the Sun-like star Kepler-90,

some 2,500 light-years from Earth. The newly discov-

ered exoplanet, named Kepler-90i, is a rocky world

with a surface temperature of roughly 800 degrees

Fahrenheit (426 degrees Celsius) that zooms around

its host star once every 14.4 days.

The discovery of Kepler-90i, as well as the discov-

ery of another exoplanet known as Kepler-80g, was

made using the first neural network designed to

search through archival data from the Kepler space

telescope. “A neural network is a machine learning

algorithm that is very loosely inspired by the human

brain,” said Christopher Shallue, senior software

engineer at Google AI and co-author of the study. He

explained that the algorithm takes sample inputs,

learns to identify patterns in the data, and then uses

those patterns to make future identifications.

Before the new neural network could analyze the

Kepler data, researchers had to first train it to spot

transiting exoplanets from Kepler’s light curves,

which show how the brightness of a star drops off

when an orbiting planet passes in front of it. Using

15,000 previously confirmed exoplanet signals as

flash cards, the neural network “learned” to cor-

rectly identify true planets. After the neural net-

work knew what patterns it was looking for, the

researchers turned it loose on 670 of Kepler’s

weaker signals. In these weak signals, the AI found

two likely exoplanets — Kepler-90i and Kepler-80g.

“Just as we expected, there are exciting discover-

ies lurking in our archived Kepler data, waiting for

the right tool or technology to unearth them,” said

Paul Hertz, astrophysics division director at NASA,

in a press release. “This finding shows that our data

will be a treasure-trove available to innovative

researchers for years to come.” — J.P.

BRIEFCASE

SPYING ON SCULPTOR
Using the Hubble Space Telescope
and the Gaia satellite, astronomers have
measured the exact 3-D motions of indi-
vidual stars within the nearby Sculptor
Dwarf Galaxy. The measurements, which
are more accurate than any others gath-
ered for a galaxy beyond the Milky Way,
provide astronomers with an observa-
tional test of current cosmological mod-
els. The results, published November 27
in Nature Astronomy, also allowed
researchers to more accurately map the
trajectory of the Sculptor Dwarf Galaxy,
showing that it revolves around the Milky
Way in a much more elliptical orbit than
previously thought.

• UNEXPECTED NURSERY
  Surprising new observations from the
  Atacama Large Millimeter/submillimeter
  Array (ALMA) show that the area immedi-
  ately around the Milky Way’s supermas-
  sive black hole contains low-mass stars.
  Despite extremely powerful tidal forces
  and harsh high-energy radiation, astron-
  omers detected the telltale signs of 11
  low-mass stars forming within 3 light-
  years of our galaxy’s 4 million-solar-mass
  black hole, known as Sagittarius A*. The
  results, published November 28 in The
  Astrophysical Journal Letters, suggest that
  the young protostars form with the help
  of outside forces, which compress the
  gas clouds despite the violent setting.


• 
  

  DARK TRACES
  Considering that dark matter is presumed
  to account for over a quarter of the uni-
  verse’s mass, scientists would really love
  to catch a glimpse of it. And although the
  elusive material has evaded direct detec-
  tion thus far, astronomers reported a tan-
  talizing hint in a November Nature paper.
  Using China’s Dark Matter Particle
  Explorer (DAMPE), a team of researchers
  detected 1.5 million cosmic ray electrons
  and positrons and plotted them against
  their energies, expecting to see a smooth
  distribution. However, according to the
  study, the DAMPE data confirmed an
  anomalous break in the curve, potentially
  corresponding to the indirect decay
  signal of a hypothetical form of dark mat-
  ter known as weakly interacting massive
  particles (WIMPs). — Jake Parks

  
  

Artificial intelligence discovers exoplanet

HEAVY METAL IN THE UNIVERSE

THIRD ROCK. Kepler-90i, an exoplanet recently discovered using Google AI technology, is the third planet in a system

with at least eight total planets. The system also has a similar configuration to our solar system, where small planets lie

near the star and larger planets are farther away. NASA/AMES RESEARCH CENTER/WENDY STENZEL

Lead, usually considered “heavy,”

barely makes the top 20, registering

as the 18th-densest element.

ATOM I C WE IG HT WATCH E R S. When you think about the 92 naturally occurring elements, logic
might dictate that No. 92 — uranium — is the heaviest. Actually, six elements are heavier (more dense)
than uranium. Those atoms have a smaller diameter, so they pack more weight per unit volume.
So, by weight (or density), here are the top 10. — Michael E. Bakich

ASTRONOMY

: ROEN KELLY

The 2018 Breakthrough Prize in Fundamental Physics awarded to the

Wilkinson Microwave Anisotropy Probe team for its detailed image

of the cosmic microwave radiation left behind by the Big Bang.

FOOD FOR THOUGHT. Researchers presented new evidence that the icy shell around Europa may experience plate

tectonics similar to those on Earth, bolstering the case for a habitable subsurface ocean beneath its frozen crust.

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