Australian Sky & Telescope - 04.2019

http://www.skyandtelescope.com.au 7

HELIOPAUSE: NASA / JPL-CALTECH / GSFC; YUTU 2: CNSA

Voyager 2 enters interstellar space

Voyager 2 crosses the heliopause.

Chang’e 4 explores the lunar farside

VOYAGER2HASBECOMEthe second

probetobreakthroughtointerstellar

space,missionscientistsannounced

December10atameetingofthe

American Geophysical Union in

also saw a sharp uptick in cosmic rays

— high-speed atomic particles that

whiz around the galaxy — as well as

an increase in the ambient magnetic

field. This confluence of events gave

mission scientists confidence that

the probe had finally broken out of

the heliosphere, a bubble of space

surrounding the Sun in which the solar

wind reigns supreme.

This marks the second time that a

spacecraft has crossed this threshold.

Voyager 1 crossed the heliopause in

2012. However, its plasma detector
      had stopped working back in 1980.
      Now, with Voyager 2 joining its twin in
      interstellar space, scientists will be able
      to obtain the first direct measurements
      of the ionised gas that drifts between
      the stars. Voyager 2 will also provide a
      second measure of the flux of galactic
      cosmic rays that impinges on the Solar
      System. Mission scientists anticipate
      another five to 10 years of operations
      for the aging probes.
      ■ CHRISTOPHER CROCKETT

crafts roughly two weeks of illumination

before sunset in late January; heating

units will keep both of them warm

duringlunarnight.Throughoutthe

three-month mission, the Queqiao

(Chinese for ‘magpie bridge’) orbiter will

relaytheprobes’datafromitshaloorbit

aroundtheL2Lagrangianpoint60,

km past the Moon.

Inadditiontoexaminingitsnew

home with a battery of instruments,

Chang’e4carriesasmallcontainer

with three species of plant seeds,

fruitflylarvaeandyeast.Thisstudent

experiment will measure how an

enclosed mini-ecosystem fares in low

gravity.Thelanderwillalsocarryout

low-frequency radio observations. The

Chinesespaceagencyhascommitted

toanopendatapolicyforthismission,

though it’s not yet clear how the data

will be released.

Laterthisyear,theheavierChang’e

5 lander and sample return capsule is

expected to join its smaller sibling on

the Moon. However, this mission still

awaits a return to flight for the Long

March 5 heavy-lift rocket.

■ DAVID DICKINSON

See videos of Chang’e 4 and Yutu 2 at

https://is.gd/Change4landing.

Yutu 2, from the Chang’e 4 lander

Heliosphere

Voyager 1

Voyager 2

Heliopause

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Washington, D.C.

A plasma detector aboard Voyager 2

recorded a sharp decline in the speed

of the solar wind on November 5.

Around the same time, the spacecraft

THE CHINESE SPACECRAFT Chang’e 4

(named for the Chinese Moon goddess)

has landed softly on the farside of the

Moon — the first mission to accomplish

this milestone.

The spacecraft launched on

December 7, 2018, and touched down

in Von Kármán crater on January 3

at 2:26 UT. The 180-km-wide crater

is one of the few flat areas within the

South Pole-Aitken Basin. This basin

was created in one of the Solar System’s

largest impacts, which might have

smashed through the crust and exposed

the lunar mantle. Exploring this region

may reveal information about the

formation and structure of the Moon.

The lander snapped images of the

terrain around it, then the Yutu 2 rover

(Chinese for ‘jade rabbit’) rolled down

its ramp later that same day.

The spacecraft landed around local

lunar sunrise, giving the solar-powered