Sky and Telescope - June 2015 - 12

News Notes

RON MILLER

EXOPLANETS I Gap Reveals Potential Exomoon

Artist's conception of the ring system circling the young giant planet or brown dwarf J1407b.
The rings are shown eclipsing the parent star, J1407, as they would have appeared from Earth's
perspective in early 2007. Analysis suggests more than 30 individual rings around J1407b.

Astronomers have conﬁrmed that the
star 1SWASP J140747.93-394542.6 (hereafter J1407) seems to have a substellar companion with a gigantic ring system, inside
which an "exomoon" might be forming -
potentially the ﬁrst detection of a satellite
forming around an exoplanet.
Ring formation is thought to be fairly
common for larger planets, as all of the
outer solar system planets have rings.
Furthermore, astronomers think that the
giant planets' major moons formed in
souped-up versions of these ring systems.
In 2012, Matt Kenworthy (Leiden
Observatory, The Netherlands), Eric
Mamajek (University of Rochester),

and colleagues discovered one of these
circumplanetary disks around the companion of the 16-million-year-old K5 star
J1407. Kenworthy and Mamajek have now
performed a new analysis of their original data, obtained by the SuperWASP
planet search.
As the companion, named J1407b,
passes between Earth and its host star, a
rich and intricate eclipse pattern occurs,
in contrast to the typical dips seen for a
single companion. Reported in the February 20th Astrophysical Journal, the new
analysis shows more than 30 separate
ring structures, within a ring system
spanning 1.2 astronomical units and

having a mass on the order of 100 Moons.
(Saturn's rings total roughly a thousandth
the Moon's mass.)
Perhaps even more exciting is the
team's conﬁrmation of one large, clear
gap in the ring around J1407b, potentially
carved out by a forming moon. The gap's
size implies a satellite mass between that
of Earth and Mars, with an orbital period
of approximately two years.
Astronomers estimate that the orbital
period of J1407b is about 10 years, but
unfortunately they don't know exactly
when the next eclipse will happen. "It
could be tomorrow, next year, a few years,
we don't know," says Mamajek. Amateur
observations reported to the American
Association of Variable Star Observers
(AAVSO) have already ruled out some
orbital periods, and the team encourages
amateur astronomers to continue to help
them monitor J1407. Such additional
observations would help detect the next
eclipse by the rings and also constrain
the companion's period, size, and mass,
as well as the size and mass of the rings.
Find more info at http://is.gd/j1407b.
■ JOHN BOCHANSKI

W
Watch a video simulation showing the
c
complicated light pattern the team
b
observed as J1407b's rings passed in front of
the star: http://is.gd/exomoondisk.

METEORITES I Long-Lived Magnetic Fields Left Their Mark
THE TRUSTEES OF THE NATURAL HISTORY MUSEUM, LONDON

The magnetic ﬁelds in the asteroid parents of two meteorites lasted hundreds of
millions of years after our solar system's
formation, an order of magnitude longer
than expected, James Bryson (University
of Cambridge, UK) and colleagues report
in the January 22nd Nature.
The team studied the famous meteorites Imilac and Esquel, found in South
America in 1822 and 1951, respectively.
The Esquel meteorite consists of gem-quality
olivine embedded within an iron-nickel matrix.

June 2015 sky & telescope

Both meteorites are pallasites, which
come from the core-mantle boundary
of a once-molten asteroid. When this
molten conducting ﬂuid inside the asteroid solidiﬁed, it locked inside itself an
imprint of the magnetic ﬁeld that existed
at that time. This imprint also exists in
the meteorites from the asteroid.
Using nanoscale imaging, the team
looked at the physical structure of tetrataenite, an iron-nickel alloy, in each meteorite. Analogous to the way tree rings
chronicle droughts and times of plenty,

http://www.is.gd/j1407b http://www.is.gd/exomoondisk

Sky and Telescope - June 2015

Table of Contents for the Digital Edition of Sky and Telescope - June 2015