The past few months have seen several

important missions launched or brought

to an end. Perhaps the most significant

of the newcomers is the long-awaited Space

Infrared Telescope Facility (SIRTF). The fourth

and last of NASA’s Great Observatories. It even-

tually lifted off on 25 August; ten days later

NASA released test images taken by the infrared

array camera. It was expected to take about a

month to focus and fine-tune the telescope.

SIRTF was planned as a space telescope for

infrared astronomy, to be launched and serviced

by the Space Shuttle. After the Challenger dis-

aster, the observatory was redesigned. The sci-

entific payload includes a wide-field and

high-resolution camera covering the 2–30 µm

region, a multi-band imaging photometer at

3–700 µm, and an infrared spectrometer. After

about three months of checks, SIRTF will begin

to study circumstellar dust clouds, brown

dwarfs, infrared galaxies and quasars and is

expected to operate for up to five years. The

mission is seen as an important bridge to

NASA’s Origins Programme (sirtf.caltech.edu/).

The SMART way to study the Moon

Europe’s first lunar expedition got under way

on the night of 27/28 September, when

SMART-1 lifted off. As the first mission in the

new series of Small Missions for Advanced

Research in Technology, its main purpose is to

demonstrate innovative technologies for future

deep-space missions, particularly the Solar

Electric Primary Propulsion system. Its ion

engine relies on the Hall effect to accelerate

xenon ions to speeds of up to 16 000 km h–1. It

can deliver 70 mN of thrust over many months,

with a specific impulse (the ratio between thrust

and propellant consumption) 5 to 10 times bet-

ter than traditional chemical engines.

Over the next four months SMART-1 will

spiral away from the Earth, then perform three

gravity-assist manoeuvres during lunar

approaches in December 2004, January and

February 2005. It enters a near-polar elliptical

lunar orbit in March 2005, ready to start sci-

ence operations in April. During this 18-month

transfer phase, the propulsion system will be

closely monitored by the Spacecraft Potential,

Electron & Dust Experiment (SPEDE) and the

Electric Propulsion Diagnostic Package. The

SPEDE experiment will also study how the solar

wind affects the Moon. Other new technologies

include a Li ion modular battery, a X/Kα-band

Telemetry and Telecommand Experiment and

an autonomous navigation technique .

The 19 kg science payload includes the

British-built Demonstration Compact Imaging

X-ray Spectrometer (D-CIXS), which will pro-

vide the first global chemical map of the Moon,

and the X-ray Solar Monitor (XSM) that will

perform spectrometric observations of the Sun

and provide calibration data to D-CIXS. Also

on board are the Advanced Moon Micro-

Imaging Experiment, a CCD camera that will

image the surface at high resolution, and the

SIR infrared spectrometer to map surface com-

position and search for water and carbon diox-

ide ice in polar craters (sci.esa.int/smart-1).

Goodbye Galileo

Scientists said goodbye to an old friend on 21

September when Galileo plunged into Jupiter’s

equatorial atmosphere at a speed of about

48 km s–1, after 14 years in space. Hundreds of

former Galileo project members and their fam-

ilies were present at the Jet Propulsion

Laboratory when the spacecraft disintegrated at

11.57 a.m. PDT. The Deep Space Network

tracking station in Goldstone received the last

signal 46 minutes later. Galileo had travelled

approximately 4.6 billion km since its launch in

October 1989. Overcoming the loss of its high-

gain antenna, a malfunctioning tape recorder

and exposure to over four times the amount of

radiation it was designed to withstand, Galileo

revolutionized our view of the Jovian system

with a series of momentous discoveries.

In October 1991 it flew past Gaspra, returning

Mission update

6.29December 2003 Vol 44

Hello Moon,goodbye JupiterThe last Great Observatory takes its place, Europe heads for the Moon,

and Galileo ends its Jovian adventure. Peter Bond reports.

Space shorts

� BERYLLIUM MIRROR FOR JWST. After a

six-month evaluation, NASA has selected

a beryllium-based mirror technology for

the 6.5 m primary mirror of the James

Webb Space Telescope (JWST). Ball

Aerospace & Technologies Corp. of

Boulder, Colorado, will begin production

of the mirror in the coming year. The

design comprises 18 hexagonal segments,

which will be incorporated into optical

assemblies, mounted on the telescope

structure, and tested at cryogenic temper-

atures, individually and as an integrated

system. The JWST mirror will be 2.5

times the diameter, yet weigh only one-

third as much, as its counterpart on the

HST. Scheduled for launch in 2011,

JWST is expected to be orders of magni-

tude more sensitive than ground-based

infrared telescopes (www.jwst.nasa.gov).

� INDIAN MOON MISSION. The

Chandrayan-1 mission, announced by the

Indian Prime Minister during his

Independence Day address, will be India’s

first foray into deep space. The 525 kg

satellite will be launched in 2008, using a

modified version of the Polar Satellite

Launch Vehicle. From a 100 km polar

orbit, Chandrayan-1 will image the lunar

surface using a mapping camera with

5 m spatial resolution and 40 km swath,

a Hyper-spectral Imager, a Lunar Laser

Ranging Instrument, a Low Energy X-ray

spectrometer for measuring fluorescent

X-rays emanating from the lunar surface

and a high-energy X-ray mapping cam-

era. It could also carry up to 10 kg of

instruments from other countries (www

.isro.org/chandrayaan-1/index.html).

� SIX SMALL SATELLITES. Six small satel-

lites were launched into low Earth orbit

on 27 September by a Russian Cosmos

launcher, including three spacecraft of the

Disaster Monitoring Constellation

(DMC). These satellites, built for

Nigeria, Turkey and the UK by Surrey

Satellite Technology Ltd, will join

AlSAT-1, another Surrey-built satellite

which was launched for Algeria last

November. The fifth and final DMC

satellite will be launched for China in

2005. Each satellite will provide 32 m

multispectral imaging anywhere on the

Earth’s surface. Together they will trans-

form the ability of international disaster

relief organizations to monitor and pro-

vide rapid response to emergencies (www

.berkeley.edu/news/media/releases/2003/

09/15_spear.shtml).

1: Galileo burns up at the end of its mission.

the first ever close-up image of an asteroid. Less

than a year later, it imaged another main-belt

asteroid, Ida, and found Dactyl, the first

known asteroid moon. In 1994 the spacecraft

made the only direct observation of comet

Shoemaker-Levy 9’s collision with Jupiter.

Before reaching Jupiter it released the first

probe to make in situ studies of the planet’s

clouds, winds and atmospheric composition. It

then made the first observation of ammonia

clouds in another planet’s atmosphere and

observed thunderstorms many times larger

than those on Earth, with lightning strikes up

to 1000 times more powerful. It was also the

first spacecraft to spend long enough in a giant

planet’s magnetosphere to identify its global

structure and internal dynamics. Galileo deter-

mined that Jupiter’s ring system is formed by

dust kicked up as interplanetary meteoroids

smash into the planet’s four small inner moons.

It also investigated Jupiter’s four largest

moons: Ganymede, Callisto, Io and Europa. Io

was found to be very volcanically active, gen-

erating lava hotter than any found on Earth

today. Europa could be hiding a salty ocean up

to 100 km deep beneath its frozen surface, con-

taining about twice as much water as all the

Earth’s oceans. Ganymede and Callisto may

also have a salty liquid layer, while Ganymede

was the first satellite found to possess a mag-

netic field. After 35 orbits the spacecraft was

deliberately put on a collision course with

Jupiter, to avoid any chance of an unwanted

impact with Europa, which would contaminate

its pristine environment (galileo.jpl.nasa.gov).

Cassini tests Einstein’s theory

An experiment by Italian scientists, using data

from NASA’s Cassini spacecraft, has confirmed

Einstein’s theory of general relativity with a pre-

cision 50 times greater than previous measure-

ments. The experiment, reported in the 25

September issue of Nature, took place in the

summer of 2002, when the spacecraft and Earth

were more than 1 billion km apart and on

opposite sides of the Sun. The researchers

observed the frequency shift of radio waves to

and from the spacecraft as the waves passed

near the Sun, and measured precisely the

change in the round-trip time of the signal. Past

tests of general relativity using the Viking lan-

ders on Mars confirmed Einstein’s prediction to

an accuracy of one part per thousand, whereas

the Cassini experiment confirmed it to an accu-

racy of 20 parts per million. Radio “noise”

caused by the solar corona and interplanetary

plasma was overcome by fitting Cassini and the

34 m diameter antenna at Goldstone with mul-

tiple links at different frequencies. In addition,

the “noise” from Earth’s atmosphere was con-

siderably reduced by special equipment installed

at Goldstone. The experiment is part of a series

planned during Cassini’s cruise to Saturn,

including the search for low-frequency gravita-

tional waves (saturn.jpl.nasa.gov).

Faint KBOs and more moons for Uranus

During recent probes of the outer solar system,

the Hubble Space Telescope has discovered two

tiny moons close to Uranus and three of the

faintest, smallest objects ever beyond Neptune.

Hubble’s Advanced Camera for Surveys

revealed that S/2003 U1, the larger of the two

moons, measures 16 km across and orbits

Uranus between Puck and Miranda. S/2003 U2

is about 12 km wide, the smallest Uranian

moon yet found. Orbiting just 300 to 700 km

from the moon Belinda, it inhabits a densely

crowded region that contains 11 other satellites

discovered in Voyager 2 pictures. S/2003 U2 is

74 800 km from Uranus and circles the planet

in 14 hours and 50 minutes. The HST observa-

tions also confirmed the discovery of

S/1986 U10, another tiny moon that was found

in 1999 during studies of Voyager pictures by

Erich Karkoschka (University of Arizona).

S/1986 U10 is 750 miles (1200 km) away from

Belinda (hubblesite.org/newscenter/2003/29).

The three Kuiper Belt Objects were found

after a 15-day search of a region in the con-

stellation Virgo. Named 2003 BF91, 2003 BG91

and 2003 BH91, they are between 25 and

45 km across – the smallest objects ever found

beyond Neptune. At 29th magnitude, these icy

bodies are a billion times fainter than the

dimmest objects visible to the naked eye.

Finding so few KBOs was a surprise for the sci-

entists, who expected to find at least 60 of such

small Kuiper Belt members. “This makes it dif-

ficult to understand how so many comets

appear near Earth, since many comets were

thought to originate in the Kuiper Belt,” said

Gary Bernstein (University of Pennsylvania).

“This is a sign that perhaps the smaller plan-

etesimals have been shattered into dust by col-

liding with each other over the past few billion

years,” (arxiv.org/abs/astro-ph/0308467).

The X-ray Moon

Our own Moon has recently been seen in a new

light after Chandra observed X-rays from the

illuminated waxing crescent and detected oxy-

gen, magnesium, aluminium and silicon over a

large area of the lunar surface, arising from

X-ray fluorescence. The same Chandra data

have also solved the mystery of X-rays that

appear to come from the dark side of the Moon,

first recorded by ROSAT in 1990. They had

been tentatively ascribed to energetic electrons

from the Sun striking the lunar surface.

However, Chandra’s observations indicate that

the X-rays originate near Earth. “The observed

X-ray spectrum, the intensity of the X-rays, and

the variation of the X-ray intensity with time,

can all be explained by emission from Earth’s

extended outer atmosphere, through which

Mission update

6.30 December 2003 Vol 44

Space shorts

� HST SUPERNOVAE SAY NO QUINTESSENCE.

A unique set of 11 distant Type Ia super-

novae studied with the Hubble Space

Telescope has something to say about

dark energy, according to the recent find-

ings of the Supernova Cosmology Project

(SCP) published in the AstrophysicalJournal. Light curves and spectra from the

11 exploding stars constitute “a strikingly

beautiful data set, the largest such set col-

lected solely from space,” according to

Saul Perlmutter (Lawrence Berkeley

National Laboratory). The study re-

inforced the remarkable discovery,

announced by the SCP in 1998, that the

expansion of the universe is accelerating

due to a mysterious energy that pervades

all space. However, the observations

revealed no anomalous effects of host-

galaxy extinction at great distances, con-

firming the value of more remote

supernovae as standard candles. Among

the numerous attempts to explain the

nature of dark energy, some are allowed

by these new measurements – including

the cosmological constant originally pro-

posed by Einstein – but others are ruled

out, including some of the simplest models

of the theories known as “quintessence”

(www.arxiv.org/abs/astro-ph/0309368).

� HUBBLE SPIES ROSETTA’S COMET. The

Hubble Space Telescope is helping scien-

tists to prepare for ESA’s ambitious

Rosetta comet mission. Observations

made with the Wide Field Planetary

Camera 2 in March 2003 have provided

precise measurements of the size, shape

and rotational period of comet

67P/Churyumov-Gerasimenko, the new

target for Rosetta. This information is

essential if Rosetta is to rendezvous with

the comet and then land a probe on its

nucleus. About 60 Hubble images of

comet 67P/C-G were taken over a period

of 21 hours between 11 and 12 March.

They showed that the nucleus is ellip-

soidal, measuring approximately 5×3 km,

with a rotation rate of approximately 12

hours. “Although 67P/C-G is roughly

three times larger than the original Rosetta

target (comet 46P/Wirtanen), its highly

elongated shape should make landing on

its nucleus feasible, now that measures are

in place to adapt the lander package to the

new scenario,” said Philippe Lamy

(Laboratoire d’Astronomie Spatiale).

Rosetta’s launch is scheduled for February

2004, with a rendezvous with the comet

about 10 years later (hubble.esa.int/).

Chandra is moving,” said Brad Wargelin (CfA).

In the new model, collisions of heavy ions of

carbon, oxygen and neon in the solar wind with

atmospheric hydrogen atoms tens of thousands

of kilometres above the surface of Earth give

rise to these X-rays. In the collisions, the solar

ions capture electrons from hydrogen atoms.

The solar ions then produce X-rays as the cap-

tured electrons drop to lower energy states

(chandra.harvard.edu).

Deep survey of galaxies

As part of the Great Observatories Origins

Deep Survey (GOODS), the HST has joined

forces with Chandra to trace the evolution of

tens of thousands of galaxies and their stellar

populations over a wide range of distances and

ages. The HST observations show that the

galaxies’ sizes increase continuously from about

1 billion years to 6 billion years after the Big

Bang. They also indicate that the rate of star

birth increased by about a factor of three

between the time the universe was about 1 bil-

lion years old and 1.5 billion years old, and

remained high until about 7 billion years ago,

when it quickly dropped to one-tenth of the ear-

lier rate. This confirms that major galaxy build-

ing trailed off when the universe was about half

its current age, and is consistent with “bottom-

up” models in which galaxies grow through

mergers with smaller galaxies.

The Chandra observations allow astronomers

to study the history of black holes over almost

the entire age of the universe. One of the key

findings in this deepest ever X-ray image is the

discovery of black holes with no optical coun-

terparts. “We found seven mysterious sources

that are completely invisible in the optical with

Hubble,” said Anton Koekemoer (STScI).

“Either they are the most distant black holes

ever detected, or they are less distant black holes

that are the most dust-enshrouded known, a

surprising result as well.” When comparing the

HST and Chandra fields, astronomers also

found that active black holes in distant, rela-

tively small galaxies were rarer than expected.

This may be due early generations of massive

stars that exploded as supernovae, evacuating

galactic gas and thus reducing the supply of gas

needed to feed supermassive black holes in these

galaxies. The results from the GOODS project

are to be published in the Astrophysical Journal(hubblesite.org/news/2003/18).

Chandra “hears” a black hole

The first sound waves from a supermassive

black hole have been found by Chandra. The

waves are thought to have been produced by

explosions in Perseus A, the huge galaxy at the

centre of the Perseus cluster, 250 million light

years away. The 2002 Chandra observation

shows ripples in the gas filling the cluster,

evidence for sound waves that have travelled

hundreds of thousands of light years from

Perseus A’s central black hole.

“We have observed the prodigious amounts of

light and heat created by black holes, now we

have detected the sound,” said Andrew Fabian

(Institute of Astronomy, Cambridge). In musi-

cal terms, the pitch is B flat, but a human could

not hear the black hole because the note is 57

octaves lower than middle C – the deepest note

ever detected. Previous Chandra observations of

the Perseus cluster showed two bubble-shaped

cavities – each about 50 000 light years across

– extending away from the black hole. These

X-ray cavities, which are also bright radio

sources, are created as jets push back the gas.

They have long been suspected of heating the

surrounding gas, through some unknown mech-

anism. Sound waves could be the answer. A

tremendous amount of energy is needed to gen-

erate the cavities, as much as the combined

energy from 100 million supernovae. Much of

this is carried by the sound waves and should

dissipate in the cluster gas, keeping it warm and

possibly preventing a cooling flow. If so, the

pitch of the sound wave would have remained

roughly constant for 2.5 billion years.

Cosmic X-ray flashes

Astronomers using X-ray, radio and optical tele-

scopes have solved the origin of objects known

as X-ray flashes (XRFs), finding that they orig-

inate from blue star-forming galaxies. This dis-

covery, reported in the Astrophysical Journal,ends speculation that XRFs are generated by

ancient γ-ray bursts whose light had been red-

shifted by the expansion of the universe. The

XRFs in this study were originally detected by

the now-defunct Beppo-SAX telescope. They

are relatively rare compared to other bursting

sources – about one detected per day. Each flash

comes from a seemingly random position on the

sky and lasts for tens to hundreds of seconds.

Locating the sources required careful coordi-

nation of Chandra, the HST and the Very Large

Array (VLA). Chandra and the VLA provided

a precise location of the fading X-ray and radio

“afterglows” of two X-ray flashes known as

XRF 011030 and XRF 020427. The HST was

used to identify and study galaxies at these loca-

tions and estimate their distances. “Now that

the very distant origin has been ruled out, X-ray

flashes could be due to exploding massive stars,

just like γ-ray bursts,” said Joshua Bloom (CfA).

“But the explosion from an X-ray flash would

need to contain less matter or less energy than

a typical γ-ray burst. Alternatively, X-ray flashes

could be γ-ray bursts viewed off-axis.” An

examination of galaxies that have hosted the

XRFs hints at a stellar origin. “Those two

galaxies in which the flashes occurred are

incredibly blue,” said Pieter van Dokkum (Yale

University). Since a galaxy’s blue colour is a

crude measure of the rate of star formation, he

says “these XRF hosts are churning out stars at

an appreciable rate for their size”.

Cannonball pulsar

Astronomers have captured an image of the

Geminga pulsar flying through space at high

speed. This first clear image of a pulsar’s X-ray

bow shock, obtained by ESA’s XMM-Newton

observatory, also shows twin X-ray tails stretch-

ing some 3 billion km from the tiny neutron

star. “We have this spectacular view because

Geminga is travelling almost directly across our

line of sight,” said Patrizia Caraveo (IASF-

CNR, Milan). “The tails appear to be the bright

edges of a three-dimensional shock wave

sculpted by Geminga, like the wake of a ship

travelling across the ocean.” The shock wave

both compresses the gas in the interstellar

medium and boosts Geminga’s magnetic field

by a factor of four. Caraveo’s team calculated

that electrons must get whipped around in the

enhanced magnetic field and then shot out, cre-

ating the X-rays that XMM-Newton found.

Astronomers had assumed that all the electrons

would be converted into γ-rays near Geminga,

but the X-ray tails show that many escape.

The intensity and angle of the tails confirm

earlier optical measurements of Geminga’s

proper motion, velocity, radius, and mass. The

density of nearby interstellar matter is indicated

by the brightness and thickness of the tails.

This observation of Geminga may also pro-

vide clues to the nature of unknown γ-ray

sources. Of the 271 higher-energy γ-ray objects

detected by the EGRET telescope on the

Compton Gamma Ray Observatory, 170

remained unidentified in other wavebands.

These mystery objects could be “γ ray pulsars”

like Geminga, with optical and X-ray emissions

invisible because they are much further

away. These results were published in Science(universe.nasa.gov/press/geminga/). �

Peter Bond is the RAS Press Officer (Space Sciences).

Mission update

6.31December 2003 Vol 44

2: The Geminga pulsar – just 12 miles across – fliesthrough space at 20 times the speed of sound, withtwin tails of X-ray light nearly two billion mileslong. Geminga, in the constellation of Gemini, is theclosest known pulsar to Earth, about 500 lightyears away (ESA/XMM-Newton/Caraveo et al.).