Astronomy

34 ASTRONOMY • JANUARY 2018

Beta Pic b’s Hill sphere stretches roughly
the distance between the Sun and Earth.
Any rings would have to be enormous for
astronomers to spot them from our world.
And if any gaps like those seen in the rings
around J1407’s planet show up, they could
be clues to the presence of exomoons. “The
potential for seeing exomoons by seeing the
path they cleared is very exciting and very
plausible,” says Kenworthy.

A worldwide hunt
Beta Pic’s southern location limits observa-
tions because the Southern Hemisphere
houses far fewer telescopes than its north-
ern counterpart. So Wang decided to take

the search to space. Working with his

adviser, Paul Kalas, also from UC Berkeley,

Wang has targeted the transit with the

Hubble Space Telescope several times.

Hubble got its first glimpse in mid-June,

when it searched for material orbiting the

infant planet. The space observatory took

its second look in early August. Wang says

their initial analysis of the data shows noth-

ing. But the team has three more observa-

tions scheduled between early October and

late November (after this issue went to

press), and Wang remains optimistic about

finding material around Beta Pic b.

Wang isn’t the only one studying the

planet with Hubble. Paul Wilson, a

researcher at France’s National Center for

Scientific Research, is using the instrument

to study the makeup of comets around the

distant star. His project searches for the

absorption signatures of exocomets

imprinted in the spectrum of Beta Pic.

Wilson is intrigued to see if the amount

of water and other ingredients varies

within the Hill sphere, much as lighter

compounds in Earth’s atmosphere drift

higher above our planet’s surface. To spot

atoms like hydrogen, nitrogen, carbon,

and oxygen, Wilson must probe at far-

ultraviolet wavelengths, which are visible

only from space because Earth’s atmo-

sphere absorbs them. Wilson and his col-

leagues also hope to study the motion of

gas and dust around Beta Pic b. If a moon

orbits this planet, the team could help

determine its natal material.

Far smaller than Hubble is the Bright

Target Explorer Constellation (BRITE-

Constellation), an array of nanosatellites

studying the brightest stars in the sky. The

first of the five 8-inch (20 centimeters) tele-

scopes launched in February 2013 to study

stellar quakes. Just like earthquakes help

reveal the internal structure of our planet,

starquakes can reveal what’s happening

inside a star.

Konstanze Zwintz, a stellar scientist at

Austria’s University of Innsbruck, previ-

ously studied Beta Pic with BRITE-

Constellation. Now she has the star in her

sights again. Her goal was to map its oscil-

lations precisely before the transit began.

Observations of the Hill sphere need to

account for Beta Pic’s pulsations. Zwintz’s

models should help other researchers

remove the variations of light that come

from the star, leaving behind only traces of

a ring or moon. Although she won’t actu-

ally study the star during the transit, the

oscillations should remain constant over

the short period. “In principle, the mecha-

nism acts like a clock for a very long time,”

says Zwintz.

Although Hubble could catch a glimpse

of a moon as large as Io or Ganymede, two

of Jupiter’s largest satellites, the odds are

against it. Astronomers would have to be

incredibly fortunate to spot a two-day tran-

sit while the space telescope is pointed at

Beta Pic b.

And ground-based observatories

couldn’t provide a lot of help, particularly

during the transit’s early stages. Beta Pic

climbs highest in the Southern Hemisphere

sky late in the calendar year, so it was

essentially beyond the reach of earthly

instruments until August.

The Antarctic Search for Transiting Exoplanets

observed Beta Pictoris under pristine skies

throughout the long southern winter. This

view shows the Milky Way rising above the

telescope’s dome. EOIN MACDONALD/IPEV/PNRA