Astronomy

Antihydrogen

n^ =^2

n^ =^1

n = 3

Photon

Nucleus

(antiproton)

Positron

Positron

energy

levels

24 ASTRONOMY • JANUARY 2018

Swirls and waves of red-tinged clouds, white oval-shaped storms
mixed with tan-toned vortices — these are some of the incred-
ible details that the JunoCam instrument is capturing at Jupiter.
The images made a splash across the news and social media in
2017, and for good reason: Never before have human eyes seen
the features JunoCam is revealing. And it’s all because of a late
decision to add this public outreach instrument.
Like all NASA space missions, Juno has a set of science objec-
tives, but none of those objectives requires a visible-light cam-
era. The craft is equipped with seven other instruments to reveal
the deep layers of Jupiter’s atmosphere, map the planet’s mag-
netic and gravitational fields, and study its aurorae. However,
those instruments and their collected data don’t always reso-
nate with the public. A chart showing the abundance of water at
different depths of Jupiter’s atmosphere doesn’t have the same
impact on non-scientists as a stunning photograph of Jupiter’s
Great Red Spot.
The mission leader, Scott Bolton, recognized that fact. Prior
to launch, Juno got one more instrument: a small camera to
engage the public. JunoCam has fewer resources than the
science instruments. There’s no large dedicated planning or

processing team. “Our concept was that the public would be

our virtual imaging team,” says Candice Hansen, the scientist

responsible for planning and operating JunoCam. That means

the public recommends imaging targets, then discusses and

votes on which ones to study — all via the internet. Once

JunoCam captures the images, members of the public process

them. The entire concept has been successful “beyond our wild-

est dreams,” says Hansen.

JunoCam has received the most attention, but Juno’s other

instruments have also been hard at work. In May, the mission

team released the first science results. Scientists knew Jupiter

has a strong magnetic field — that’s why Juno’s electronics have

to be well-shielded to protect against radiation damage — but

Juno has found it is twice as strong as expected. The magnetic

field is also “lumpy” — it’s stronger in some places than others.

Researchers think that could mean the field is generated not at

the very center of the planet, but closer to the surface.

Juno flies by Jupiter every 53 days, skimming a few thousand

miles above the cloud tops at each pass. Its primary mission

includes 12 of these 53-day orbits and continues through July

2018. NASA could then opt to extend the mission.

When the universe came into existence

13.8 billion years ago, equal amounts of

matter and antimatter should have been cre-

ated. Look around the cosmos now, and it’s

obvious matter stuck around, and antimat-

ter didn’t. While scientists don’t know why

there’s a preference for matter, learning more

about antimatter will help reveal the answer.

But it’s not easy. Whenever antimatter

encounters its matter match, the two annihi-

late. (For example, when an electron encoun-

ters an antielectron, called a positron, they

are converted into a burst of radiation.) So

scientists have to find a way to isolate anti-

matter from matter.

Juno and its outreach camera

Spying

light from

antimatter

When electrons transition between

energy levels in an atom, they either

absorb or release specific wavelengths

of light. The ALPHA collaboration

has measured a positron transition in

antihydrogen, and found its wavelength

identical to hydrogen. ASTRONOMY: ROEN KELLY