The life and times of Stephen Hawking

Today, Hawking is one of the world’s leading thinkers on cosmology and the history and evolution of the universe. ANDRÉ PATTENDEN/COURTESY STEPHEN HAWKING

All of us astronomy types owe a lot more to Stephen
Hawking than I think most of us realize. He has been
at the forefront of thinking on cosmology, gravitation,
black holes, and related subjects for many years.
Many of us know that Hawking had for years,
until 2009, held the Lucasian Professorship of
Mathematics at the University of Cambridge, the
same chair occupied 300 years earlier by Isaac
Newton. Just a few years ago, Hawking founded
and became the first director of the Centre for
Theoretical Cosmology at Cambridge.

Most of us know his life story reasonably
well, particularly in the wake of the
2014 film The Theory of Everything, which
depicted his struggle for knowledge and
survival. The movie brought home an
Academy Award for actor Eddie Redmayne.
Obviously, Hawking’s story of triumph
and brilliance is deeply intertwined
in the public perception with his debilitating
motor neuron disease, diagnosed in
1963 when Hawking was 21 years old.
That such a combination of sheer brilliance
exists in a body that has withstood
an incredible attack of nature is overwhelming
and inspiring to us all.
Knowing that you’re in the room with
perhaps the smartest human being on the
planet is an amazing experience. Last year,
Hawking attended the Starmus Festival in
the Canary Islands, the unique gathering
of science enthusiasts that features talks by
Nobel Prize winners, astronaut-explorers,
science communicators, and researchers,
as well as celebrations of music, art, and
life on Earth. He delivered two incredible
talks, one on the creation of the universe
and the other on black holes. He sat near
the front in the audience during my talk
about recent astronomical advances and
the communication of science to the public.
Trust me, there is a magnetic feeling
one has when Hawking sits close by.
Now, a year later, we are both on the
Board of Directors of the Starmus Festival.
And I am proud to say that due to the
herculean efforts of Garik Israelian,
the founder and director of
Starmus, that next year, in
June 2016, the third Starmus
Festival will take place, again
in the Canaries. And this
time it will constitute a major
tribute to Stephen Hawking, his
life and times. It will be an experience
in the world of astronomy, cosmology,
physics, and entertainment like
no other that has come before it.
Despite all we know about Hawking,
there is something more there. Something
almost magical. Let me explain.
Humble beginnings
Stephen William Hawking was born
January 8, 1942, in Oxford, England, in
the midst of World War II and the ongoing
blitz bombing by the Nazis. He was
descended from a line of tenant farmers,
his father being the first to attend college,
at Oxford, where he studied medicine.
His mother was the daughter of a Scottish
doctor. To the day, Hawking was born 300
years after Galileo’s death. At first, however,
no one suspected he would become
attached to the heavens.
The family had spent time in Oxford
rather than always staying home in London
because the former was off-limits for Nazi
bombing, along with Cambridge (as were
the German university towns of Heidelberg
and Göttingen). In Highgate, North London,
the Hawking family grew. “My earliest
memory is of standing in the nursery
of Byron House School in Highgate and
crying my head off,” Hawking says in his
memoir, My Brief History (Bantam, 2013).
Discomfort from being left with strangers
splayed against the trauma of an occasional
bomb dropped nearby. “A V-2 rocket
landed a few houses away from
ours,” he says.
Hawking grew up enjoying
his train set and later built
model airplanes and ships.
After the war, in 1950, the
family moved to St. Albans, 20
miles north of central London,
so that Hawking’s father could be
close to the newly opened National
Institute for Medical Research, where he
studied tropical diseases. In St. Albans,
“the family was regarded as eccentric,” says
Hawking. The Hawkings weren’t poor, but
they were of relatively modest means.
Education in England was very hierarchical,
and Hawking did well enough to
be classed fairly high but stayed in public
schools. During the last portion of his
normal schooling, he became interested
in mathematics and physics. Physics,
Hawking thought, was somewhat boring
“because it was so easy and obvious.” But
physics and astronomy offered the hope
of understanding the meaning of it all.
“I wanted to fathom the depths of the
universe,” he says.
How to make a physicist
In 1959, at age 17, Hawking took an
entrance exam for Oxford. He received
a scholarship and commenced schooling
there, in his third year joining the boating
club as a coxswain in order to make more
friends. He didn’t work particularly hard,
averaging an hour of studying per day,
but that was the prevailing attitude then
at Oxford. One should rely on brilliance.
Despite that, he advanced successfully to
graduate school.
In October 1962, Hawking arrived at
Cambridge as a grad student, having
applied to work with the great astronomer
and cosmologist Fred Hoyle. He ended up
working with Dennis Sciama and was
excited by the prospects of cosmology
and elementary particle physics. Particle
physics was in a strange period of research,
so Hawking gravitated toward cosmology
and gravitation, two seemingly neglected
fields that offered lots of opportunity.
Hawking joined the battle to expand
the understanding of general relativity just
as that movement was gaining momentum.
During his last year at Oxford, however, he
noticed increased clumsiness. He saw a
physician after falling down some stairs,
and the doctor merely warned him to “lay
off the beer.” But while skating on a
frozen lake at St. Albans, he fell
and could not get back on his
feet. Just after his 21st birthday,
Hawking entered a hospital
for tests.
The doctors at first were
not too communicative, but
soon Hawking was diagnosed
with an incurable, rare type of a motor
neuron disease in the vein of ALS, “Lou
Gehrig’s disease,” that has since paralyzed
him. “The realization that I had an incurable
disease that was likely to kill me in
a few years was a bit of a shock,” says
Hawking. That is certainly something of
an understatement. Some of the doctors
initially thought he would only live for a
couple years. That was 52 years ago, and he
is still going strong.

Marriage and family
Hawking had met Jane Wilde, a friend
of his sister’s, just before his diagnosis,
and the two wanted to get married. If
so, he would need a job. And for that, he
would need to finish his Ph.D. Set against
the background of an uncertain future,
Hawking thrust into high working gear for
the first time. Hawking was inspired by
Roger Penrose, who hypothesized spacetime
singularities in the centers of black
holes, and applied this thinking to the
entire universe in his Ph.D. dissertation,
which he completed in
1966. Meanwhile, the previous
year, he married Jane.
The Hawking family grew.
Son Robert was born in 1967,
daughter Lucy in 1970, and later,
another son, Timothy, in 1979.
At the tail end of the 1960s and
throughout the 1970s, Hawking worked
tirelessly on gravitational waves and their
likely sources (black holes), on the confirmation
of the Big Bang theory, and on a
theory of causal structure in general relativity,
and became increasingly interested
in black holes. A few days after the birth of
his daughter, Hawking realized he could
apply some of the work he had done with
causal theory to black holes. He also had
published significant work on the meaning
of general relativity, showing among other
things that it would break down at singularities,
i.e. in black holes.
General relativity and
black holes
Hawking next turned to attempting to
combine general relativity, the behavior of
the very large, with quantum theory, the
behavior of the very small. He used black
holes as the theoretical test bed for quantum
behavior. How would quantum fields
scatter off of a black hole? His calculations
demonstrated, much to his astonishment,
that a black hole would show some emission,
not simply scattering.
This finding showed that a previously
unknown relationship must exist between
thermodynamics — the science of heat —
and gravity. Hawking had discovered that
over time radiation leaks away from a black
hole, eventually evaporating it. This came
to be known as Hawking radiation.
Hawking’s calculations showed that the
radiation leaking from black holes would
be thermal and random. But the evaporating
black hole left a paradox at the heart of
physics. How could the radiation left over
carry all the information about what made
the black hole? And if the information was
lost, that would seem to be incompatible
with quantum physics. Hawking believes
that information is not lost, but it is simply
not returned in a meaningful way.
In the early 1970s, Hawking spent time
doing research with his good friend Kip
Thorne at the California Institute of
Technology, and the Hawking family
enjoyed the Golden State. He graduated
from a mechanical to an electric wheelchair,
and taking care of him became a
family affair. Back to England in the mid-
’70s, the Hawkings continued to focus on
their many family activities as Stephen’s
condition gradually worsened.
Complexity and challenge
By the 1980s, the Hawkings’ marriage
had become strained, and Jane began to
have romantic feelings for a church organist
she knew, Jonathan Hellyer Jones. He
moved in with the family to help take care
of Hawking, who did not object, thinking
the family would need someone to care for
them when he was gone. Hawking began
to have choking fits, and during a Swiss
trip in 1985, was rushed to the hospital and
placed on a ventilator. Surgeons had to perform
a tracheotomy, meaning Hawking’s
ability to speak, already badly degraded,
would now be completely gone.
Now Hawking could only communicate
by learning to spell out words one letter at
a time on a spelling card using eyebrow
motions to indicate choices. It was, needless
to say, exceptionally frustrating at first
and required countless hours of practice.
One of the greatest minds the world has
known was in danger of being completely
cut off from the rest of us, still functioning
magnificently, but in danger of no clear
channel of communication.
Moreover, Hawking had become upset
with the increasing closeness of Jane and
Jonathan. He moved out, into a flat, in
1990. One of his nurses, Elaine Mason, who
he had grown close to over hours of caregiving,
moved in with him. Five years later
they were married, and Hawking declared:
“It’s wonderful — I have married the
woman I love.” He has subsequently stated
that several times, Elaine has saved his life.
In 1982, Hawking had the idea to write
a popular level book about his research on
the universe, and the subsequent title, A
Brief History of Time, was an incredible
runaway best-seller. Rather than his technical
publisher, Cambridge University Press,
Hawking sold the book to Bantam, wanting
to reach as large a market as he could.
Following the huge success of his book,
Hawking turned to another spectacular
subject in physics, the possibility of time
travel. In 1990, Hawking’s friend Thorne
had posited that perhaps time travel would
be possible by passing through wormholes
(black holes that could be used as ways to
travel in time or space). Can the laws of
physics allow a wormhole and space-time
to be so warped that a spaceship could
enter it and return to its own past? Could
an advanced civilization construct a time
machine by modifying a small part of
space-time so that it closed time-like
curves of space in a finite region?
Theoretically, the answer depends on
the model you use and also the assumptions
you make about various conditions
within it. But, to quote Hawking, “the
future looks black for time travel, or should
I say blindingly white?” It does not appear
that the laws of physics allow for traveling
back in time, regardless of the space-time
curvature. “Even if some different theory is
discovered in the future,” says Hawking, “I
don’t think time travel will be possible.”
Over time, Hawking has come to live
with his disability with increasing success.
He has moved to a more sophisticated
wheelchair and to progressively better systems
of computer communication. His
accomplishments in theoretical physics,
cosmology, astrophysics, and related fields
have formed a new basis for understanding
relativity and the origin and fate of the cosmos,
a century after the heyday of Einstein.
One could rightly ask the question: How
is it that Stephen Hawking has not been
awarded a Nobel Prize?
Hawking’s mind is of course as sharp as
ever. This was witnessed most recently by
astronomy enthusiasts from his two gripping
talks at Starmus.

Starmus 3: A Tribute to
Stephen Hawking
Hawking’s presence at Starmus 2, in
September 2014 in the Canary Islands,
sets up an amazing next iteration of the
world’s greatest science festival. For those
not familiar with Starmus, the gathering
was founded by astronomer Garik Israelian
and features a board of directors including
astrophysicist and Queen guitarist Brian
May, cosmonaut Alexei Leonov, evolutionary
biologist Richard Dawkins, musician
Peter Gabriel, and Hawking himself.
The first Starmus took place in 2011, the
second last year, and the third and greatest
thus far is planned for June 27–July 2, 2016.
Nearly 1,000 people attended Starmus 2
in Tenerife and La Palma, enjoying stellar
talks from a who’s who of scientists, astronaut-
explorers, and artists.
Starmus 3 will be far bigger yet,
with the theme constituting a tribute to
Hawking and his life in science. The event,
which is expected to draw on the order of
1,800 people, will be titled: “Beyond the
Horizon: Tribute to Stephen Hawking.”
Nothing like Starmus 3 has ever taken
place before. Ten Nobel Prize-winning scientists
will be delivering talks, including
astrophysicists Adam Riess and Brian
Schmidt (co-discoverers of dark energy);
astrophysicist Robert Wilson (co-discoverer
of the cosmic microwave background radiation);
chemists Harry Kroto (discoverer of
buckminsterfullerene) and Eric Betzig (fluorescence
microscopy); physicist David
Gross (particle physics); biologists Carol
Greider and Elizabeth Blackburn (DNA
enzymes); and Edvard Moser and
May-Britt Moser (brain cell
physiology).
Moreover, incredible
astronauts and astronomers
also will speak at the festival.
They include Leonov, the first
human to walk in space;
Apollo astronaut Rusty
Schweickart; cosmonaut Sergey
Volkov; astronauts Chris Hadfield, Garrett
Reisman, and Michael López-Alegría;
and astronomers Lord Martin Rees, Kip
Thorne, Jill Tarter, Robert Williams, Neil
deGrasse Tyson, and Neil Turok. Other bigname
speakers will be announced soon.
The festival also will include time spent
at the 10.4-meter Gran Telescopio Cana rias,
the world’s largest optical telescope, not to
mention observing under some of the best
skies on Earth. Plus, attendees won’t want
to miss the Sonic Universe Concert featuring
Brian May and other special guests.
Says Hawking: “With this next edition,
Starmus confirms its position as a unique
debating chamber for the future of the
human race.” It is an event filled with intellectual
exploration, amazing astronomy,
music, and fun, and is structured so that
attendees can spend time with these leading
lights of science. This is what
makes the festival unique. For
more details on Starmus, see
www.starmus.com.
Hawking’s life, to be celebrated
in a special way next year,
casts an enormous example onto
the world for those of us who adore
the universe. He has shown, time and
again, that the power of the human mind
has a unique ability — to outstretch troubles
and challenges in our everyday world,
to aspire to and to reach a greater understanding
of ourselves on Earth.
That’s why all humans owe something
to Hawking. He has been not only one of
the brightest minds we have ever seen, but
also a shining example of the best ideals of
humanity. Let the celebration begin.

David J. Eicher is editor of Astronomy and is
proud to be a member of the Starmus Festival
Board of Directors, as well as a lifelong admirer
of Stephen Hawking.

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TOP 10 SPACE STORIES of 2015

Astronomers find signs of dark matter close to home, unravel the mystery of a famous supernova, and take a trip to Pluto. by Liz Kruesi

Planetary science drew the most attention in 2015, and for good reason. Mysterious bright spots on the largest asteroid in our solar system puzzled scientists. The spacecraft following a comet as it hurtled toward and then retreated from the Sun continued to make surprising discoveries. And, of course, the year saw the history-making and expectation-shattering observations of Pluto.

But discoveries about celestial objects beyond the solar system deserve attention, too. The center of the Milky Way Galaxy harbors a mysterious glow from dead stars or something even stranger, while astronomy’s most studied stellar explosion is changing before our eyes. Each year, Astronomy ranks the top 10 astronomical discoveries and space stories. Here’s where 2015’s biggest ones fall.

10. The Red Planet under water
The rovers and orbiters
at Mars have uncovered
plenty of evidence that
the planet once had liquid
water on its surface, from etched
river gullies and dried-up shorelines to
minerals that need water to form. But a
new study, some five years in the making,
confirms that the Red Planet hosts
liquid water on its surface today. Since
2010, Lujendra Ojha, from Georgia State
University, and colleagues have used
Mars Reconnaissance Orbiter (MRO)
data to study streaks running down
martian crater walls. They suspected
that the streaks, called “recurring slope
lineae,” which appear to lengthen from
one image to the next, mark flowing
salt water. But they didn’t have proof.
In the new study, published in the
September 28 issue of Nature Geoscience,
Ojha’s team provides the spectral
signature (from MRO) of
salty water at four locations of
recurring slope lineae on the
Red Planet’s surface — confirming
that flowing water is present
today on Mars.
While little water remains today,
scientists know that it must have been
bountiful in the past. A study published
in the April 10 issue of Science analyzed
how much water the planet once had.
Researchers used several Earth-based
telescopes to look at the martian atmosphere
in infrared light. Geronimo
Villanueva of NASA’s Goddard Space
Flight Center and colleagues were looking
for specific colors: one that corresponds
to normal water (H2O) and one
that comes from a heavier form of water
that has an extra neutron (hydrogendeuterium-
oxygen, or HDO).
The scientists mapped the
ratio of these two
types of water
three times over six years (or three martian years) to
compare the water in the atmosphere at
different seasons.
H2O is lighter than HDO and thus
evaporates more easily. So by measuring
the ratio of the two, the researchers
could calculate how much water Mars
has lost over time, and thus how much
water it would have started with.
Villanueva’s team says that 4.5 billion
years ago, some 6 million cubic miles
(23 million cubic kilometers) of water
pooled in a northern ocean covering
nearly 20 percent of the surface. This
martian ocean would have been a bit
larger than Earth’s Atlantic Ocean.
This is more water than many
researchers had expected. “[Mars] was
very likely wet for a longer period of
time than previously thought,” said
co-author Michael Mumma of
NASA in a press statement,
“suggesting the planet
might have been habitable
for longer.”

9. Dark matter hints next door
The invisible and perplexing
material that makes up at least
80 percent of our universe’s mass
keeps leaving clues for astronomers,
but not enough to solve its
identity. While scientists do not
know yet what makes up this
dark matter, one search method
has given tantalizing hints over
this past year.
Scientists believe that when
two dark matter particles collide
they destroy themselves
— a process called annihilation
— and create other familiar
particles. Among this shower
of particles is gamma radiation.
And nearby dwarf galaxies are
an ideal place to look for darkmatter-
produced gamma rays.
“[Dwarf galaxies] are calm,
quiet places; we don’t know any
reason why they should be emitting
high-energy gamma rays on
their own,” says Carnegie Mellon
University’s Alex Geringer-
Sameth, lead scientist of one of
the searches. “Therefore, if you
see some gamma rays coming
from one of these dwarf galaxies,
it is very exciting because it
could be a sign that dark matter
is annihilating within it.”
This past year, a sky survey
uncovered nine dwarf galaxies
within 1 million light-years of
the Milky Way. And one of the
galaxies from this Dark Energy
Survey (DES) was a prime dark
matter target: Reticulum II.
Geringer-Sameth’s team and
another — Dan Hooper and
Tim Linden, both of the
University of Chicago — used
seven years of data from the
Fermi Gamma-ray Space
Telescope to find that this dwarf
galaxy looks a bit brighter than
it should in gamma rays. “We
provide an indication that
something is emitting gamma
rays from the direction of
Reticulum II, and that something
seems to be consistent
with dark matter annihilation,”
says Geringer-Sameth. “While
the signal from Reticulum II is
tantalizing, it would be premature
to conclude it has a dark
matter origin.”
Hooper and Linden calculated
a similar chance that the
signal has dark matter origins.
“You might call that evidence;
you won’t call that a discovery,”
Hooper says of the studies. “We
really need more data to resolve
the issue.” Scientists expect
DES to uncover some 20 more
nearby dwarf galaxies, and
future surveys will find even
more. Scientists will then be
able to compare archived Fermi
gamma-ray data with these
dwarf galaxies to see if they have
a signal similar to Reticulum II’s.

8. Supernova hunters see quadruple
In November 2014, Patrick Kelly was looking through his
team’s recently collected Hubble Space Telescope images of
galaxy cluster MACS J1149.6+2223 when something stood
out: four stars with exactly the same pattern of light surrounding
one of the cluster’s member galaxies. “I knew it
was a big discovery,” says Kelly, a postdoctoral fellow at the
University of California, Berkeley. He emailed his group
about the find, and they have since confirmed it as a supernova
whose image has been distorted by the cluster galaxy,
which lies along the supernova’s line of sight. Months of
observations have classified this object as a type IIp supernova,
which originated from a massive star.
The distant stellar explosion lies more than halfway across
the observable universe. Its light left the supernova some
9.5 billion years ago. Along its path to Earth, the light encountered
a massive member of the intervening galaxy cluster. The
galaxy warps the fabric of space-time like a bowling ball
warps a trampoline, and so the supernova’s light follows those
curves in space-time, detoured from its path to Hubble.
This “gravitational lensing” causes the light to appear to
come from four different points instead of just one lone
supernova. Norwegian astrophysicist Sjur Refsdal predicted
this type of quadruple-lensed supernova 50 years
ago. The 2014 discovery, published in the March 6, 2015,
issue of Science, has been named Supernova Refsdal after
that scientist.
In his 1964 paper, Refsdal said such a blast could help to
measure the rate our universe is expanding. Because the
explosion’s images show up in four locations, light followed
four different paths to arrive at Hubble. Astronomers can use
each of those paths to map the distribution of normal material
and unseen dark matter in the galaxy cluster. In addition,
those different paths are related to the cosmic expansion rate.
Another spectacle awaits the team. All of those paths also
take a different travel time. After creating a map of MACS
J1149.6+2223, the astronomers realized that the supernova
should have taken a fifth path, too. The light is still traveling
and could appear as early as late 2015, says Kelly.

7. Deciphering a famous supernova
In February 1987, a brilliant new point
of light shone in the southern sky. This
turned out to be the explosive blast marking
the death of a star and earned the name
Supernova 1987A. Lying just 168,000 lightyears
from Earth, it is the closest supernova
to explode since astronomers developed the
tools to study such a blast. And that proximity
makes it a perfect laboratory to watch
how supernovae evolve. Several discoveries
published in 2015 reveal changes to the
blast site and uncover secrets of the explosion
first seen 28 years ago.
SN 1987A is recognized by its ring of
bright nodules, like shining diamonds
along a band. These brilliant spots mark
where the blast’s shock wave is slamming
into previously shed material. While
astronomers had seen the diamonds brightening
for the past 15 years, new observations
show them fading for the first time.
This means the blast’s shock wave is passing
through the ring of material, breaking
it apart. Visible-light observations made
by Stockholm University’s Claes Fransson
and colleagues using the Hubble Space
Telescope show the ring is fading, while
spots outside of the ring are beginning to
light up. They described the observations
in the June 10 issue of The Astrophysical
Journal Letters.
X-ray images from the Chandra X-ray
Observatory also show the ring’s light
changing. David Burrows, who has been
watching SN 1987A evolve for 15 years, says
the blast’s high-energy light is plateauing.
Another 2015 study focused on SN
1987A’s guts.
When a star at least 10 times the Sun’s
mass explodes at the end of its life, the
energies, temperatures, and pressures are
so high that the supernova produces a
range of heavy chemical elements. One of
those is titanium-44 (Ti-44), which is an
unstable radioactive isotope. “The isotope
is produced deep in the core of the explosion,
and its properties — mass, ejection
speeds, and distribution — directly reflect
the physics in the core,” says Steve Boggs of
the University of California, Berkeley.
Like all elements, Ti-44 glows with
specific colors of light, so if scientists look
for those colors, they can learn where that
material is. But none of Ti-44’s colors had
been visible to astronomers until a recent
X-ray telescope, the Nuclear Spectroscopic
Telescope Array (NuSTAR), opened its
eyes and began collecting data.
Boggs and colleagues described in the
May 8 issue of Science their study using
NuSTAR to map Ti-44 in SN 1987A.
The element’s distribution is clumpy and
uneven, implying that the explosion was
off-center. This is the second supernova
remnant the team has been able to probe;
the other is Cassiopeia A. Both explosions
were asymmetrical, Boggs’ team says, which
means now astronomers have to rethink the
theoretical models of these blasts.
Most computer models have assumed a
symmetrical blast, but the new studies prove
something more complex is happening.

6. Water abounds in the outer solar system
Saturn’s moon Enceladus continues to show why it’s one of the best
bets in the solar system to search for life. Astronomers have suspected
for years that salty water dredged up from a subsurface sea spews
into space out of fissures near the moon’s south pole. But an analysis,
published online September 11 in the journal Icarus, of seven years
of images from NASA’s Cassini spacecraft indicates that Enceladus
has a subsurface global ocean instead of merely a regional sea.
Cornell University planetary scientist Peter Thomas and colleagues
measured a slight wobble in the moon’s rotation. If
Enceladus were solid, its mass would dampen that motion. The
researchers believe, instead, that a liquid water ocean lies between
the moon’s icy surface layer and the rocky interior. They say the
ocean is deeper and the ice shell thinner at the south polar region,
where Cassini has spied some 100 geysers of salt water.
Scientists think that to keep any material in liquid state within
Enceladus’ interior requires the push-and-pull tidal energy from
Saturn. A global ocean is harder to keep warm than a regional sea,
and so this discovery could also indicate that the saturnian satellite
has more tidal energy than originally thought. “If that is correct,”
says team member Carolyn Porco, “and its ocean has been
around a long, long time, then it may mean that any life within it
has had a long time to evolve.”
Some of the material spewing from Enceladus’
underground ocean flows out through the geysers,
flows toward Saturn because of the planet’s gravitational
pull, and then orbits the planet as its E ring.
In the March 12 issue of Nature, Frank Postberg at
the universities of Heidelberg and Stuttgart in
Germany and colleagues described how they used
the Cassini spacecraft to study some of the material
from the E ring. They saw silicon-rich molecules
(called silicates) just a few nanometers wide. When
this type of material is found in space, it almost
always originates from rock being dissolved in
water. But to learn the precise characteristics of that
water-rock interaction, Postberg’s team collaborated
with researchers from Japan to mimic the conditions
needed at Enceladus to produce the sizes and composition of silicate particles they observed. They found the
water needs to be at least 194° F (90° C) and have a pH between 8.5
and 10.5. These characteristics imply hot-spring-heated water; the
only other place where such hydrothermal vents have ever been
seen is on Earth, and these sites host extreme organisms.
The chemical reaction that produces the silicates also creates
molecular hydrogen, and a different instrument on board Cassini
will look for this gas during a late 2015 flight through Enceladus’
plumes. If it detects more molecular hydrogen than expected, it will
confirm hydrothermal activity, says Postberg.
This year, astronomers also found the best evidence so far of
water at yet another location in our solar system: Jupiter’s large
moon Ganymede. NASA’s Galileo spacecraft, which studied the
jovian system in the late 1990s and early 2000s, studied Ganymede’s
magnetic field to learn whether the moon holds a global ocean
under its surface. But the analysis from only 20 minutes of flyby
observations was inconclusive. Fast forward to the past year, when
Joachim Saur of the University of Cologne and his colleagues studied
data from two 7-hour Hubble Space Telescope observations.
Ganymede has an auroral belt in each hemisphere just like
Earth does. Jupiter’s magnetic field also influences these aurorae
and causes them to rock during Jupiter’s 10-hour rotation period.
Saur’s team knew that if Ganymede did not have
an ocean, the aurora belts would change their positions
slightly, tilting about 6°. “However, when a
salty and thus electrically conductive ocean is present,
this ocean counterbalances Jupiter’s magnetic
influence and thus reduces the rocking of the auroras
to only 2°,” says Saur. “We observed Ganymede
with the Hubble Space Telescope for more than
five hours and saw that the aurora barely moved
and rocked by only 2°. This thus confirms the existence
of an ocean.” The researchers think the
ocean lies about 90 miles (150km) below the
moon’s rock-ice crust and is about 60 miles
(100km) thick. This strong evidence of Ganymede’s
ocean continues to increase the number of worlds
in our solar system known to host water.

5. Ceres takes center stage
Since March 6, NASA’s Dawn spacecraft has been in orbit around Ceres,
the largest object in the asteroid belt lying between Mars and Jupiter. For
a full recap of the spacecraft’s adventures and discoveries, see “Dawn mission
reveals dwarf planet Ceres” (p. 44). Dawn will continue its studies
until June 2016. Ceres is the second asteroid Dawn has orbited; the first was
Vesta, between July 2011 and September 2012.
Ceres’ pockmarked surface is riddled with craters like those seen at
Saturn’s icy moons. “The features are pretty consistent with an ice-rich
crust,” said Dawn planetary geologist Paul Schenk of the Lunar and
Planetary Institute in Houston in a press statement. The spacecraft has
mapped the heights of surface features like craters and mountains.
Bright spots on the dwarf planet’s surface also have mystified planetary
scientists. These reflective regions first came into view at the beginning of
2015 and have since resolved into a multitude of spots. They sit within
Ceres’ northern Occator Crater, which spans 57 miles (92km) and is
2.5 miles (4km) deep. Researchers at first believed they were ices or salts,
but bad luck repeatedly stymied their efforts to gain spectra of the mysterious
spots. Based on the reduced reflectivity of the spots, however, the consensus
is turning to salt.
In August, Dawn had reached its penultimate orbit, circling Ceres
from 910 miles (1,470km) out. A few months later, the spacecraft will have
transitioned to its final science
orbit, at just 230 miles (375km)
above the surface.
In addition to mapping the surface
and measuring the heights of
the mountains and craters on Ceres,
Dawn is working to learn about the
composition of materials on the
asteroid’s surface. The spacecraft
also is measuring how different
locations on Ceres pull with more or
less gravity. The answers will let scientists
map the world’s gravity and
learn how the dwarf planet’s rocky
interior is distributed.

4. Youngest cluster of galaxies seen
The process of forming clusters of galaxies is
not one that astronomers can watch in real time
because it takes billions of years. Instead, they
look for galaxy clusters at different stages in their
development. Because light travels at a constant
speed, the light collected from more distant
objects means scientists are seeing those objects
further back in time. In 2015, astronomers reported
they had found the youngest cluster yet, still in
an early stage of formation.
To find this protocluster, Joseph F. Hennawi of
the Max Planck Institute for Astronomy in
Heidelberg and colleagues searched for the
extremely bright centers of galaxies hosting
actively feeding supermassive black holes. These
quasars, as they are known, are used in two ways:
first, as markers for large galaxies, and second, as
flashlights to see through nearby gas clouds. Such
gas clouds glow because they absorb the active
galaxy’s light and then re-emit it. The researchers
were looking for a specific color of light that energized
hydrogen throws out, called Lyman alpha.
They spied four active galaxies near to one
another on the sky. When they studied their light
in more detail, they saw all four lie the same distance
from Earth and the light from these objects
has been traveling for 10.6 billion years. No one
had ever seen, nor expected to find, four quasars
in the same gravitationally bound group, so this
discovery was a surprise.
The team also saw these galaxies embedded in
an enormous cloud of hydrogen. The conglomeration
existed when the universe was just about
3.2 billion years old, and the gas clump stretches
about 1 million light-years across. “It’s 100 percent
clear that it’s a protocluster,” says team member J.
Xavier Prochaska of the University of California,
Santa Cruz. “It’s a structure that will evolve into
something like [the] Virgo [Cluster] today.”

3. A surprise glow at the galaxy’s center
When astronomers have a
new telescope that can resolve
types of light never seen before,
they can usually expect a surprise.
And that’s exactly what
the Nuclear Spectroscopic
Telescope Array (NuSTAR)
uncovered when it collected
a million seconds worth of
high-energy X-ray light from
the center of the Milky Way.
Astronomers found a diffuse
glow, but they can’t pin down
what’s causing it.
Kerstin Perez was using
NuSTAR data to study the glowing
material around a neutron
star lying in the galactic center.
But she couldn’t get rid of a
pervasive signal in the central
13 light-years by 26 light-years.
Once she convinced herself and
her colleagues that this signal
truly exists, they went to work to
figure out what it could be.
NuSTAR doesn’t just take
pictures; it also spreads the
light out in a spectrum, collecting
information about the
intensity of light at each individual
color to make it easier
to analyze. To figure out what
creates the haze the researchers
saw, they considered types
of objects that would give
a similar light pattern, says
Perez. “And then you think,
how many of those objects
would you have to have in
order to make up how bright
we see it.” This analysis led
the NuSTAR team to four possibilities,
which they described
in an April 30 Nature article.
Three of the possibilities
are stellar remnants stealing
gas from a companion. As this
material piles up, it ignites and
glows in X-rays. The idea is that
there are so many of these pairs
that NuSTAR can’t separate
them from one another, so they
appear as a haze.
One of these types of
corpses could be thousands of
white dwarf stars, each 90 percent
of the Sun’s mass. Another
could be about a thousand
black holes and neutron stars
— the dense leftover cores of
once massive stars. And the
third option is some thousand
millisecond pulsars, which are
neutron stars that have had so
much material dumped onto
them by their companions that
their rotation rates have sped
up dramatically. The problem is
that astronomers have no idea
how so many of these objects
— whatever they might be —
could exist in a small region in
the galactic center.
The fourth possibility is
that as material falls toward the
supermassive black hole at the
center of the Milky Way, some
of it gets shot out at high speed.
This streaming material could
be interacting with nearby
clouds of gas, causing them to
glow. But the hazy glow that
NuSTAR sees doesn’t look oriented
in the right way for this
explanation.
While scientists with
NuSTAR hope that upcoming
telescopic observations can help
narrow down which of these
possibilities is responsible for
this emission, they don’t expect
to learn the answer soon.

2. Europe’s visit to a comet
The European Space Agency’s Rosetta spacecraft
has been watching how Comet 67P/Churyumov-
Gerasimenko changes as it passes through its
closest approach to the Sun and then hurtles away.
The history-making mission has revealed many
cometary secrets.
Ever since Rosetta beamed back its first images
of Comet 67P, scientists have wondered what made
its unexpected double-lobed “rubber duck” shape.
Now, they have an answer. According to a paper
published October 15 in Nature, two separate
objects collided to form the comet. To reach this
conclusion, the researchers measured how regions
were sloped, looked at the orientations of features
on the surface, and calculated the local gravity
across the surface.
Rosetta also has returned thousands of images
of Comet 67P. It has photographed boulders balancing
on just a small part of their surfaces, piles
of rubble that seem to have come from falling
rocks, and jets of gas spewing from pits dozens of
feet across possibly created by sinkholes. The
spacecraft also has spied about 120 bright areas
several feet wide on the comet’s surface, and scientists
say these are most likely patches of water ice
reflecting sunlight.
After analyzing data of one water-ice patch on
the comet’s “neck,” scientists say the area seems to
appear and disappear with the comet’s 12-hour
rotation. They think that as the region feels direct
sunlight, ice on the surface and just an inch (a few
centimeters) below are heated and turn directly to
gas — a process called sublimation. The sunlight
also warms the layers of ground beneath the
region, and so further-buried ice makes its way as
gas to the surface. As the patch rotates into darkness,
the surface cools again and the just-risen gas
turns to ice. The scientists, who reported this
water cycle in the September 24 issue of Nature,
say the process repeats each cometary day.
Rosetta’s refrigerator-sized Philae lander had
also studied the comet’s surface, even though the
sequence of events to land this spacecraft didn’t
go as planned. After dropping from Rosetta on
November 12, 2014, and bouncing several times
before finally tumbling to rest, Philae stayed alert
for just around 60 hours before falling into hibernation.
Because of its unplanned bounces, the
lander was able to compare two different sites on
the comet’s surface. The first landing site appears
to have a soft dusty material about 8 inches (20cm)
thick covering a much harder material, possibly
icy or crystalline in nature. Philae’s final resting
spot, however, lacks that dusty coating.
At the first landing location, the craft “smelled”
16 organic compounds, including four never
before detected on a comet. Another instrument
detected several gases at the same location, like
water vapor, carbon monoxide, and formaldehyde.
Comets are expected to be pristine relics from the
early solar system, but Comet 67P has more complex
chemistry than expected, and some of the
molecules discovered on the comet’s surface are
important for biology.
After hibernating for seven months, Philae
surprised everyone when it woke up again June
13. Over the next few weeks, Philae and Earth
had spotty conversations, with the last command
sent and received July 9. Scientists have no way to
know whether Philae still sits atop Comet 67P, or
whether it has been pushed off by actively spewing
jets of gas.
Rosetta will continue watching Comet 67P
through September 2016, at which point mission
scientists will most likely try to land the spacecraft
on the comet for a last look.

STORIES TO WATCH FOR IN 2016
• The European Space
Agency’s LISA Pathfinder,
a mission to test
the technologies needed
for a full-scale gravitational
wave observatory,
will begin to return
results.
• The Japan Aerospace
Exploration Agency will
launch Astro-H to study
the high-energy universe.
• NASA will launch its
Origins, Spectral Interpretation,
Resource
Identification, Security,
Regolith Explorer
(OSIRIS-Rex) asteroid
sample-return mission.
• Astronomers will begin
closing other telescopes
on Hawaii’s Mauna Kea
in order to make way for
the Thirty Meter Telescope
slated to begin
operations there in the
early 2020s.
• Juno will arrive at Jupiter
to peer through the
giant world’s thick
clouds.
• Advanced Laser Interferometer
Gravitationalwave
Observatory (LIGO)
will return data on gravitational
waves.

1. Pluto and its moons revealed
When NASA’s New Horizons spacecraft
flew by Pluto, Earth watched and celebrated.
“The target didn’t disappoint,” says
Principal Investigator S. Alan Stern. “It’s
absolutely stunning.” And even though the
science collection lasted just months, the
New Horizons mission had been decades
in the making. NASA chose the mission in
2001, the spacecraft launched in 2006, and
it reached Pluto on July 14, 2015.
Seeing the pixelated blobs of Pluto and its
largest moon, Charon, evolve into complex
worlds through the eye of New Horizons
was rewarding, satisfying, and awesome,
says Stern. That’s because everything about
Pluto surprised scientists. They expected a
frozen, cratered, and long-dead world with
an equally old-looking system of moons.
Instead, Pluto’s surface is young, with
smooth frozen plains, icy mountains as high
as the U.S. Rockies, topography that resemble
dunes, a glacial lake, and ice that has
recently flowed around other features in the
same way that glaciers move on Earth’s surface.
The scientists estimate that the
uncratered swaths of terrain are 100 million
years old, while other regions are billions of
years in age.
Pluto’s varied surface with such youthful
areas means that something internal must
be warming it to make it pliable. And while
all the objects in our planetary system would
have been warm shortly after the solar system
formed 4.5 billion years ago, scientists
didn’t think such a small object could stay
warm all these years. “We expect small planets
to typically run out of energy a lot sooner
than the big planets. It’s like a small cup of
coffee cools off faster than a bucket of coffee,”
says Stern. But what New Horizons has
revealed about Pluto, he adds, changes the
expectations of planetary geology.
Scientists have also created a map of
methane ice distribution, and this material
seems to prefer a region of young terrain
that scientists have informally named
“Sputnik Planum.” Outside of this area,
methane is still present and congregates
on crater rims and brighter regions but
avoids crater centers and darker regions for
unknown reasons.
The up-close photos of Pluto have also let
scientists precisely measure the width of the
dwarf planet: 1,473 miles (2,370km). This
secures Pluto as the largest known object
orbiting beyond Neptune.
After New Horizons flew by Pluto, it
looked back and watched the dwarf planet
eclipse the Sun. This alignment let scientists
study Pluto’s atmosphere as sunlight filtered
through it. Above the surface lie distinct
haze layers that extend to about 80 miles
(130km) out, several times farther than
researchers expected. And New Horizons
detected wisps of a nitrogen-rich atmosphere
1,000 miles (1,600km) out.
While Pluto has been the main focus,
Charon also has shown surprises. It too
has a varied surface, with some regions
void of impact craters. Cliffs stretch hundreds
of miles across the surface, indicating
the crust has fractured. A deep canyon,
4 to 6 miles (6 to 10 km) deep, also scours
Charon’s surface.
New Horizons snapped photos of Pluto’s
four smaller moons as well: Nix, Hydra,
Styx, and Kerberos. While Charon is
751 miles (1,208 km) across, each of these
four is just a few dozen miles wide.
Most of New Horizons’ data is still on
board the spacecraft and will be downloaded
piece by piece over the next several
months. Researchers will pore over the additional
data in the next few years, learning
more every day about Pluto and its moons.
Even though humans saved this dwarf
system for last in our exploration of the
solar system, just the first views exceeded
and upended expectations and have given
researchers a treasure-trove of new science.


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The long journey to Mars grows by 2 years

Despite the savvy NASA public relations campaign
tied to the release of Ridley Scott’s The
Martian, America’s beleaguered human spaceflight
program still took a step back during
September. The first launch to carry humans on
NASA’s new deep space crew vehicle has slipped
until 2023 — nearly two years later than previously
planned.
The slip isn’t the program’s first.
That crew vehicle, now known as Orion, was
first announced in 2004 following the Space
Shuttle Columbia disaster, as part of a program
that would replace previous proposed space
plane designs and return humans to the Moon “as
early as 2015.” The course was soon reimagined as
the Constellation program, and then eventually
canceled itself in 2009 after a review found it was
underfunded and far behind schedule. But not
long after, a compromise mission was announced
that would keep Orion and instead send humans
to an asteroid and on to Mars in the 2030s.
Then, in December 2014, Orion was finally
launched for the first time and became the first
crew-capable spacecraft launched beyond low-
Earth orbit since Apollo. The rocket built to carry
Orion, the Space Launch System, is due to see its
first launch in 2018. And, following more tests, the
two were set for an initial crewed launch in 2021.
But as NASA battles Congress to fully fund
the private spacecraft it has contracted to supply
the International Space Station, the agency announced
September 16 that without its requested
funds, Orion’s first crewed launch could slip some
20 months.
Some in Congress called the delay a political
tactic because NASA wasn’t getting the funding
it wanted, but the space agency says technical
hurdles have cost Orion time as well. —

Pluto surprises with blue skies, red water

Blue skies surround a dark and gloomy world
3 billion miles (5 billion kilometers) from Earth.
The first color photos of Pluto’s atmosphere
trickled back from NASA’s New
Horizons spacecraft in October, giving
astronomers fresh evidence for how the
dwarf planet’s thin veil works.
“Who would have expected a blue sky in
the Kuiper Belt? It’s gorgeous,” says New
Horizons Principal Investigator Alan Stern of
the Southwest Research Institute (SwRI) in
Boulder, Colorado.
On Earth, our blue skies are caused by
light scattering off nitrogen and oxygen molecules
in the atmosphere. But on Pluto, scientists
suspect the Sun’s faint light scatters off
soot-like particles known as tholins, which
form as ultraviolet light breaks down and ionizes
molecules like methane and nitrogen.
The actual particulates are likely gray or red,
but the scattering makes them appear blue.
As these tholins fall to the surface, they grow
by interacting with volatile ices and ionized
molecules, eventually becoming red.
New Horizons data have already shown
Pluto has an unexpectedly low surface pressure
of just 1/100,000 that of Earth — about
half of the expected value. That indicates
much of its atmosphere already has collapsed
as Pluto moves out in its elliptical orbit.
In October, the spacecraft also found the
chemical fingerprints of water ice on the surface.
Water is abundant on Pluto, but its shell
is largely covered by nitrogen and methane.
“Understanding why water appears
exactly where it does, and not in other places,
is a challenge that we are digging into,” says
New Horizons scientist Jason Cook of SwRI.
Curiously, the regions richest in water ice
are also red. “We don’t yet understand the
relationship between water ice and the reddish
tholin colorants on Pluto’s surface,”
says Silvia Protopapa, of the University of
Maryland, College Park.


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