Sky & Telescope - September 2016 - 9

EXOPLANETS I 5th Planet

PRO-AM I Astro-imagers Get Ready for Juno

IN BRIEF
ExoMars Rover Delayed Until 2020.
European and Russian oﬃcials have postponed the launch of the European Space
Agency's ﬁrst Martian rover for two years.
The ﬁrst ExoMars mission, comprising the
Trace Gas Orbiter and the Schiaparelli lander,
left Earth as planned this past March (S&T:
July 2016, p. 10). The second phase, a rover,
was scheduled to follow in 2018. But because
the same team was working on both phases,
holding to the 2018 launch date would have
forced the team to build the ﬁnal spacebound rover before completing the prototype
and ﬁnishing engineering tests - clearly
unacceptable.
■ DAVID DICKINSON

Light Echoes Map Planet-forming Disk.
Astronomers have used light's ﬁnite speed
to pinpoint the location of the "inner wall"
of the disk of dust and gas that's feeding a
growing baby star. Protostars naturally ﬂicker

Astronomical Association) urged observers to watch for a possible revival of the
planet's North Temperate Belt. This
would start with a very bright spot in that
region. After Earth-based observers identify a change, the spacecraft could follow
up to record more details.
Cooperation between amateurs
and professionals will be supported by
maintaining or improving some speciﬁc
projects and websites, including the JunoCam homepage, where amateurs can submit raw images for mission scientists to
use. Through this website the public can
also vote for features they would like Juno
to take images of. Mission scientists will
program the camera according to which
features ranked the highest.
Also in the works in the coming
months is a new version of the Planetary
Virtual Observatory and Laboratory
(PVOL) website, to facilitate image analysis. Find out more about the workshop
and how to get involved at https://is.gd/
proamjuno.

Astronomers have made the ﬁrst
high-resolution image of a cometary belt
around the young star HR 8799. The disk,
a region comparable to our solar system's
Kuiper Belt, lies outside the orbits of the
star's four known planets. But in imaging
the belt, Mark Booth (Pontiﬁcal Catholic
University of Chile) and colleagues discovered signs of a ﬁfth planet.
Previous observations found that the
disk extended from roughly 100 to 310
astronomical units. Astronomers had also
found evidence of a halo of small dust
grains. But it was hard to tell the diﬀerence
between the belt and the grains.
Using ALMA to pick up emission from
the disk's dust, Booth's team found that
the inner edge lies between 133 and 166
a.u. That's too far out to have been carved
by the outermost known planet. Instead,
the edge's location suggests that a
smaller, not-yet-detected planet is setting
the boundary, the team reports in the July
21st issue of Monthly Notices Letters of the
Royal Astronomical Society.

■ CHRISTOPHE PELLIER

■ ANA V. ACEVES

Using a Light Echo to Measure the Inner Gap in a Protoplanetary Disk

NASA / JPL-CALTECH

On May 12-13, amateurs and professionals interested in supporting NASA's Juno
mission met in Nice, France, for a workshop dedicated to projects and techniques
related to observing Jupiter.
The spacecraft arrived at the giant
planet on July 4th (S&T: July 2016, p. 18).
Although Juno will image Jupiter at very
high resolution, especially in the polar
regions, it lacks the ability to create global
portraits. So it falls to Earth-based observers to watch regions out of view from the
probe and to acquire the large-scale views
that provide context for the spacecraft's
small-scale scrutiny.
Highest on the "to-do" list for the
months ahead is to sustain the ongoing
ground-based survey of Jupiter, so lots
of discussion focused on the necessary
equipment, imaging, and processing
tools and techniques needed for that task.
For example, more and more planetary
imagers are utilizing infrared and methane-band ﬁlters, as well as atmosphericdispersion correctors.
In addition, John Rogers (British

in brightness, and the photons from these
surges reach us two ways: by ﬂying directly
at us from the star, or after ﬁrst bouncing oﬀ
the disk surrounding it (see above). The latter
are called light echoes. The delay between the
two ﬂashes reveals how far the gas is from
the central object. Observers have long used
light echoes to measure the mass of supermassive black holes, but now for the ﬁrst
time Huan Meng (Caltech) and colleagues

have used them to study a protostar, YLW
16B. By watching the star's infrared brightness change, the team caught an echo 75
seconds after its initial ﬂicker. This echo, the
authors argue in the May 20th Astrophysical
Journal, comes from an inner, dusty edge
in the disk. The time delay corresponds to a
traveled distance of about 0.08 astronomical
unit, exactly what's expected for a dusty disk.
■ MONICA YOUNG

SkyandTelescope.com September 2016

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Sky & Telescope - September 2016

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