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Space News Update — July 17, 2018 —

Contents

In the News

Story 1:

Dusk for Dawn: Mission of Many Firsts to Gather More Data in Home Stretch

Story 2:

New Research Raises Hopes for Finding Life on Mars, Pluto and Icy Moons

Story 3:

NASA Juno Data Indicate Another Possible Volcano on Jupiter Moon Io

Departments

The Night Sky

ISS Sighting Opportunities

NASA-TV Highlights

Space Calendar

Food for Thought

Space Image of the Week

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1. Dusk for Dawn: Mission of Many Firsts to Gather More Data in Home Stretch

This mosaic of Cerealia Facula in Occator Crater is based on images obtained by NASA's Dawn spacecraft in its second

extended mission, from an altitude as low as about 21 miles (34 kilometers). Credits: NASA/JPL-

Caltech/UCLA/MPS/DLR/IDA

As NASA’s Dawn spacecraft prepares to wrap up its groundbreaking 11-year mission, which has included two

successful extended missions at Ceres, it will continue to explore -- collecting images and other data.

Within a few months, Dawn is expected to run out of a key fuel, hydrazine, which feeds thrusters that control its

orientation and keeps it communicating with Earth. When that happens, sometime between August and October,

the spacecraft will stop operating, but it will remain in orbit around dwarf planet Ceres.

Dawn is the only spacecraft to orbit two deep-space destinations. It has given us new, up-close views of Ceres and

Vesta, the largest bodies between Mars and Jupiter. During 14 months in orbit from 2011 to 2012, Dawn studied

Vesta from its surface to its core. It then pulled off an unprecedented maneuver by leaving orbit and traveling

through the main asteroid belt for more than two years to reach and orbit Ceres, which it has been investigating

since 2015.

At Ceres, the spacecraft discovered brilliant, salty deposits decorating the dwarf planet like a smattering of

diamonds. The science behind these bright spots is even more compelling: they are mainly sodium carbonate and

ammonium chloride that somehow made their way to the surface in a slushy brine from within or below the crust.

These discoveries were fueled by the tremendous efficiency of ion propulsion. Dawn wasn’t the first spacecraft to

use ion propulsion, familiar to science-fiction fans as well as space enthusiasts, but it pushed the limits of this

advanced propulsion’s capabilities and stamina.

"Dawn's unique mission to orbit and explore two strange new worlds would have been impossible without ion

propulsion," said Marc Rayman of NASA’s Jet Propulsion Laboratory, Pasadena, California, who has served as

Dawn's mission director, chief engineer and project manager. "Dawn is truly an interplanetary spaceship, and it has

been outstandingly productive as it introduced these fascinating and mysterious worlds to Earth."

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These days, near the end of Dawn’s second extended mission at Ceres, the spacecraft continues to wow us week

after week, with very close photos shot from only 22 miles (35 kilometers) above the dwarf planet -- about three

times the altitude of a passenger jet.

Although the Dawn mission is winding down, the science is not. Besides the high-resolution images, the spacecraft

is collecting gamma ray and neutron spectra, infrared and visible spectra, and gravity data. The observations focus

on the area around Occator and Urvara craters, with the main goal of understanding the evolution of Ceres, and

testing for possible ongoing geology.

“The new images of Occator Crater and the surrounding areas have exceeded expectations, revealing beautiful,

alien landscapes,” said Carol Raymond of JPL, principal investigator of the Dawn mission. “Ceres’ unique surface

appears to be shaped by impacts into its volatile-rich crust, resulting in intriguing, complex geology, as we can see

in the new high-resolution mosaics of Cerealia Facula and Vinalia Faculae.”

The first results of this mission phase, which started in early June, are being presented this week at the Committee

on SPAce Research (COSPAR) meeting in Pasadena. (Website: https://www.cospar-assembly.org/ ) Raymond and

JPL scientist Jennifer Scully will offer new information on the relationships between bright and dark materials on the

floor of Occator Crater, which show impact processes, landslides and cryovolcanism.

Dawn scientists are using new high-resolution data from Dawn to test and refine hypotheses about Occator crater’s

formation and evolution. “Observations, modeling and laboratory studies helped us conclude that the bright spots

are either formed by impacts interacting with the crust, or that a reservoir of briny melt contributed to their

formation,” said Scully.

The new images so far support the hypothesis that exposure of subsurface material in that region is ongoing, and

that it is geologically active, feeding from a deep reservoir. Eleonora Ammannito of the Italian Space Agency,

deputy lead for the Dawn visible and infrared mapping spectrometer, will present updated maps at the conference

showing the distribution of briny materials across Ceres’ surface.

Also at COSPAR, Dawn flight team member Dan Grebow of JPL will describe Dawn’s final orbit, designed to abide by

NASA’s planetary protection protocols.

Source: NASA Return to Contents

This close-up image of

the Vinalia Faculae in

Occator Crater was

obtained by NASA's

Dawn spacecraft in its

second extended

mission, from an

altitude as low as 21

miles (34 kilometers).

Credits: NASA/JPL-

Caltech/UCLA/MPS/D

LR/IDA

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2. New Research Raises Hopes for Finding Life on Mars, Pluto and Icy

Moons

Based on new evidence from Jupiter’s moon Europa, astronomers hypothesize that chloride salts bubble up from the icy

moon’s global liquid ocean and reach the frozen surface. Credit: NASA/JPL-Caltech

Since the 1970s, when the Voyager probes captured images of Europa’s icy surface, scientists have suspected that

life could exist in interior oceans of moons in the outer Solar System. Since then, other evidence has emerged that

has bolstered this theory, ranging from icy plumes on Europa and Enceladus, interior models of hydrothermal

activity, and even the groundbreaking discovery of complex organic molecules in Enceladus’ plumes.

However, in some locations in the outer Solar System, conditions are very cold and water is only able to exist in

liquid form because of the presence of toxic antifreeze chemicals. However, according to a new study by an

international team of researchers, it is possible that bacteria could survive in these briny environments. This is good

news for those hoping to find evidence of life in extreme environments of the Solar System.

The study which details their findings, titled “Enhanced Microbial Survivability in Subzero Brines“, recently appeared

in the scientific journal Astrobiology. The study was conducted by Jacob Heinz from the Center of Astronomy and

Astrophysics at the Technical University of Berlin (TUB), and included members from Tufts University, Imperial

College London, and Washington State University.

Basically, on bodies like Ceres, Callisto, Triton, and Pluto – which are either far from the Sun or do not have interior

heating mechanisms – interior oceans are believed to exist because of the presence of certain chemicals and salts

(such as ammonia). These “antifreeze” compounds ensure that their oceans have lower freezing points, but create

an environment that would be too cold and toxic to life as we know it.

For the sake of their study, the team sought to determine if microbes could indeed survive in these environments by

conducting tests with Planococcus halocryophilus, a bacteria found in the Arctic permafrost. They then subjected

this bacteria to solutions of sodium, magnesium and calcium chloride as well as perchlorate, a chemical compound

that was found by the Phoenix lander on Mars.

They then subjected the solutions to temperatures ranging from +25°C to -30°C through multiple freeze and thaw

cycles. What they found was that the bacteria’s survival rates depended on the solution and temperatures involved.

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For instance, bacteria suspended in chloride-containing (saline) samples had better chances of survival compared to

those in perchlorate-containing samples – though survival rates increased the more the temperatures were lowered.

For instance, the team found that bacteria in a sodium chloride (NaCl) solution died within two weeks at room

temperature. But when temperatures were lowered to 4 °C (39 °F), survivability began to increase and almost all

the bacteria survived by the time temperatures reached -15 °C (5 °F). Meanwhile, bacteria in the magnesium and

calcium-chloride solutions had high survival rates at –30 °C (-22 °F).

The results also varied for the three saline solvents depending on the temperature. Bacteria in calcium chloride

(CaCl2) had significantly lower survival rates than those in sodium chloride (NaCl) and magnesium chloride

(MgCl2)between 4 and 25 °C (39 and 77 °F), but lower temperatures boosted survival in all three. The survival

rates in perchlorate solution were far lower than in other solutions.

However, this was generally in solutions where perchlorate constituted 50% of the mass of the total solution (which

was necessary for the water to remain liquid at lower temperatures), which would be significantly toxic. At

concentrations of 10%, bacteria was still able to grow. This is semi-good news for Mars, where the soil contains less

than one weight percent of perchlorate.

However, Heinz also pointed out that salt concentrations in soil are different than those in a solution. Still, this could

be still be good news where Mars is concerned, since temperatures and precipitation levels there are very similar to

parts of Earth – the Atacama Desert and parts of Antarctica. The fact that bacteria have can survive such

environments on Earth indicates they could survive on Mars too.

In general, the research indicated that colder temperatures boost microbial survivability, but this depends on the

type of microbe and the composition of the chemical solution. As Heinz told Astrobiology Magazine:

“[A]ll reactions, including those that kill cells, are slower at lower temperatures, but bacterial survivability didn’t

increase much at lower temperatures in the perchlorate solution, whereas lower temperatures in calcium chloride

solutions yielded a marked increase in survivability.”

The team also found that bacteria did better in saltier solutions when it came to freezing and thawing cycles. In the

end, the results indicate that survivability all comes down to a careful balance. Whereas lower concentrations of

chemical salts meant that bacteria could survive and even grow, the temperatures at which water would remain in a

liquid state would be reduced. It also indicated that salty solutions improve bacteria survival rates when it comes to

freezing and thawing cycles.

Of course, the team emphasized that just because bacteria can subsist in certain conditions doesn’t mean they will

thrive there. As Theresa Fisher, a PhD student at Arizona State University’s School of Earth and Space Exploration

and a co-author on the study, explained:

“Survival versus growth is a really important distinction, but life still manages to surprise us. Some bacteria can not

only survive in low temperatures, but require them to metabolize and thrive. We should try to be unbiased in

assuming what’s necessary for an organism to thrive, not just survive.”

As such, Heinz and his colleagues are currently working on another study to determine how different concentrations

of salts across different temperatures affect bacterial propagation. In the meantime, this study and other like it are

able to provide some unique insight into the possibilities for extraterrestrial life by placing constraints on the kinds

of conditions that they can survive and grow in.

These studies also allow help when it comes to the search for extraterrestrial life, since knowing where life can exist

allows us to focus our search efforts. In the coming years, missions to Europa, Enceladus, Titan and other locations

in the Solar System will be looking for biosignatures that indicate the presence of life on or within these bodies.

Knowing that life can survive in cold, briny environments opens up additional possibilities.

Source: Universe Today Return to Contents

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3. NASA Juno Data Indicate Another Possible Volcano on Jupiter

Moon Io

This annotated image highlights the location of the new heat source close to the south pole of Io. The image was

generated from data collected on Dec. 16, 2017, by the Jovian Infrared Auroral Mapper (JIRAM) instrument aboard

NASA's Juno mission when the spacecraft was about 290,000 miles (470,000 kilometers) from the Jovian moon. The scale

to the right of image depicts of the range of temperatures displayed in the infrared image. Higher recorded temperatures

are characterized in brighter colors – lower temperatures in darker colors. Credits: NASA/JPL-

Caltech/SwRI/ASI/INAF/JIRAM

Data collected by NASA’s Juno spacecraft using its Jovian InfraRed Auroral Mapper (JIRAM) instrument point

to a new heat source close to the south pole of Io that could indicate a previously undiscovered volcano on the

small moon of Jupiter. The infrared data were collected on Dec. 16, 2017, when Juno was about 290,000 miles

(470,000 kilometers) away from the moon.

“The new Io hotspot JIRAM picked up is about 200 miles (300 kilometers) from the nearest previously mapped

hotspot,” said Alessandro Mura, a Juno co-investigator from the National Institute for Astrophysics in Rome.

“We are not ruling out movement or modification of a previously discovered hot spot, but it is difficult to

imagine one could travel such a distance and still be considered the same feature.”

The Juno team will continue to evaluate data collected on the Dec. 16 flyby, as well as JIRAM data that will be

collected during future (and even closer) flybys of Io. Past NASA missions of exploration that have visited the

Jovian system (Voyagers 1 and 2, Galileo, Cassini and New Horizons), along with ground-based observations,

have located over 150 active volcanoes on Io so far. Scientists estimate that about another 250 or so are

waiting to be discovered.

Juno has logged nearly 146 million miles (235 million kilometers) since entering Jupiter's orbit on July 4, 2016.

Juno's 13th science pass will be on July 16.

Source: NASA Return to Contents

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The Night Sky

Wednesday, July 18

• The Moon at nightfall shines to the upper right of Spica. Look very high above the Moon for brighter

Arcturus. Far to the right of Arcturus is the Big Dipper.

• The Cygnus Milky Way is high in the east after dark and passes overhead late at night. The Heart Star of

Cygnus, and the center of the Northern Cross, is 2nd-magnitude Sadr (Gamma Cygni), smack in the Milky

Way's midst. Binoculars will show the roughly heart-shaped ring of faint stars around and including it.

Thursday, July 1

• First-quarter Moon (exact at 3:52 p.m. Eastern Daylight Time). The Moon shines in the southwest at dusk,

with Spica to its lower right and Jupiter to its left. Draw a line about twice as far onward from Jupiter and

you'll reach Antares, passing Delta Scorpii along the way.

Friday, July 20

• The waxing gibbous Moon shines over Jupiter this evening. Left of Jupiter by just 2° is the wide binocular

double star Alpha Librae, magnitudes 2.8 and 5.1.

The Moon is 1.3 light-seconds distant from us, Jupiter is 44 light-minutes in its background, and the two stars

of Alpha Librae are 77 light-years behind them.

Saturday, July 21

• Jupiter and little Alpha Librae shine lower right of the Moon this evening. To the Moon's lower left is Antares,

with other stars of upper Scorpius scattered around.

Source: Sky and Telescope Return to Contents

Tuesday, July 17

• Starry Scorpius is sometimes called "the

Orion of Summer" for its brightness and

its prominent red supergiant (Antares in

the case of Scorpius, Betelgeuse for

Orion). But Scorpius passes a lot lower

across the southern sky on July nights

than Orion does in winter (for those of us

at mid-northern latitudes.) That means it

has only one really good evening month:

July.

Catch Scorpius due south just after dark

now, before it starts to tilt lower toward

the southwest. It's full of deep-sky

objects to hunt out with a good sky atlas

and binoculars or a telescope. As the Moon passes through first quarter, it

hangs with Spica and then Jupiter.

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ISS Sighting Opportunities (from Denver)

Date Visible Max Height Appears Disappears

Wed Jul 18, 00:32 AM 2 min 17° 17° above N 11° above NNE

Wed Jul 18, 2:09 AM < 1 min 10° 10° above NNW 10° above NNW

Wed Jul 18, 3:45 AM 2 min 17° 10° above NNW 17° above N

Wed Jul 18, 5:21 AM 2 min 35° 10° above NW 35° above NW

Wed Jul 18, 10:00 PM 6 min 42° 11° above SSW 10° above ENE

Wed Jul 18, 11:37 PM 5 min 24° 11° above W 11° above NNE

Thu Jul 19, 1:16 AM < 1 min 10° 10° above NNW 10° above NNW

Thu Jul 19, 2:53 AM 1 min 13° 10° above NNW 13° above N

Thu Jul 19, 4:29 AM 6 min 48° 10° above NW 12° above ESE

Thu Jul 19, 9:09 PM 5 min 21° 11° above S 11° above E

Thu Jul 19, 10:44 PM 6 min 38° 10° above WSW 11° above NE

Fri Jul 20, 00:23 AM 3 min 12° 10° above NW 10° above NNE

Fri Jul 20, 2:01 AM < 1 min 10° 10° above NNW 10° above NNW

Fri Jul 20, 3:37 AM 6 min 29° 10° above NW 10° above E

Fri Jul 20, 5:13 AM 5 min 32° 11° above WNW 11° above SSE

Sighting information for other cities can be found at NASA’s Satellite Sighting Information

NASA-TV Highlights (all times Eastern Time Zone)

July 18, Wednesday

12:25 p.m. – Space Station In-Flight Educational Event with the St. Louis Science Center in St. Louis, Missouri,

and NASA astronaut Serena Aunon-Chancellor (All Channels)

July 19, Thursday

9:50 a.m. – Space Station In-Flight Event with the Wall Street Journal Digital Network and NASA astronaut

Serena Aunon-Chancellor of NASA Center (All Channels)

11:30 a.m. – Space Station astronauts Drew Feustel and Alexander Gerst talk with the Wall Street Journal Digital

Network (All Channels)

July 20, Friday

1 p.m. – Pre-launch Science Briefing for Parker Solar Probe (All Channels)

Watch NASA TV online by going to the NASA website. Return to Contents

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Space Calendar

Jul 17 - Comet P/2018 L4 (PANSTARRS) Closest Approach To Earth (0.859 AU)

Jul 17 - Comet 216P/LINEAR At Opposition (3.787 AU)

Jul 17 - Centaur Object 10199 Chariklo Occults 2UCAC 20033219 (13.7 Magnitude Star)

Jul 17 - Apollo Asteroid 2018 NM Near-Earth Flyby (0.004 AU)

Jul 17 - Apollo Asteroid 9162 Kwiila Closest Approach To Earth (0.831 AU)

Jul 17 - Asteroid 2362 Mark Twain Closest Approach To Earth (0.991 AU)

Jul 17 - Asteroid 7984 Marius Closest Approach To Earth (1.458 AU)

Jul 17 - Asteroid 9941 Iguanodon Closest Approach To Earth (1.564 AU)

Jul 17 - Lecture: Moon, Mars and Beyond, London, United Kingdom

Jul 17 - Webinar: Regional Climate Change Projections Science, Information and Services

Jul 18 - Comet C/2016 N6 (PANSTARRS) Perihelion (2.669 AU)

Jul 18 - Comet 94P/Russell At Opposition (3.006 AU)

Jul 18 - Comet 233P/La Sagra At Opposition (3.189 AU)

Jul 18 - Apollo Asteroid 2018 NL4 Near-Earth Flyby (0.027 AU)

Jul 18 - Amor Asteroid 2018 MH Near-Earth Flyby (0.072 AU)

Jul 18 - Asteroid 17473 Freddiemercury Closest Approach To Earth (1.735 AU)

Jul 18 - Asteroid 9674 Slovenija Closest Approach To Earth (1.788 AU)

Jul 18 - Jocelyn Bell Burnell Colloquium: A Graduate Student's Story - The Discovery of Pulsars, Sydney,

Australia

Jul 18 - Hendrik Lorentz's 165th Birthday (1853)

Jul 19 - Comet 364P/PANSTARRS Closest Approach To Earth (0.236 AU)

Jul 19 - Comet C/2017 T3 (ATLAS) Perihelion (0.825 AU)

Jul 19 - Apollo Asteroid 2018 NQ1 Near-Earth Flyby (0.042 AU)

Jul 19 - Apollo Asteroid 2018 NQ1 Near-Earth Flyby (0.042 AU)

Jul 19 - Asteroid 3229 Solnhofen Closest Approach To Earth (0.989 AU)

Jul 19 - Apollo Asteroid 5011 Ptah Closest Approach To Earth (1.450 AU)

Jul 19 - Asteroid 3115 Baily Closest Approach To Earth (1.815 AU)

Jul 19 - Asteroid 1578 Kirkwood Closest Approach To Earth (3.564 AU)

Jul 19 - Lecture: VR/AR in Space - The Next Space Revolution?, Menlo Park, California

Jul 19 - 5th Anniversary (2013), Cassini, Earth Photo

Source: JPL Space Calendar Return to Contents

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Food for Thought

From an Almost Perfect Universe to the Best of Both Worlds

The Planck’s “image” of cosmic microwave background

It was 21 March 2013. The world’s scientific press had either gathered in ESA’s Paris headquarters or logged in

online, along with a multitude of scientists around the globe, to witness the moment when ESA’s Planck

mission revealed its ‘image’ of the cosmos. This image was taken not with visible light but with microwaves.

Whereas light that our eyes can see is composed of small wavelengths – less than a thousandth of a millimeter

in length – the radiation that Planck was detecting spanned longer wavelengths, from a few tenths of a

millimeter to a few millimeters. Most importantly, it had been generated at very beginning of the Universe.

Collectively, this radiation is known as the cosmic microwave background, or CMB. By measuring its tiny

differences across the sky, Planck’s image had the ability to tell us about the age, expansion, history, and

contents of the Universe. It was nothing less than the cosmic blueprint.

Astronomers knew what they were hoping to see. Two NASA missions, COBE in the early 1990s and WMAP in

the following decade, had already performed an analogous set of sky surveys that resulted in similar images.

But those images did not have the precision and sharpness of Planck.

The new view would show the imprint of the early Universe in painstaking detail for the first time. And

everything was riding on it.

If our model of the Universe were correct, then Planck would confirm it to unprecedented levels of accuracy. If

our model were wrong, Planck would send scientists back to the drawing board.

When the image was revealed, the data had confirmed the model. The fit to our expectations was too good to

draw any other conclusion: Planck had showed us an ‘almost perfect Universe’. Why almost perfect? Because a

few anomalies remained, and these would be the focus of future research.

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Now, five years later, the Planck consortium has made their final data release, known as the legacy data

release. The message remains the same, and is even stronger.

“This is the most important legacy of Planck,” says Jan Tauber, ESA’s Planck Project Scientist. “So far the

standard model of cosmology has survived all the tests, and Planck has made the measurements that show it.”

All cosmological models are based upon Albert Einstein’s General Theory of Relativity. To reconcile the general

relativistic equations with a wide range of observations, including the cosmic microwave background, the

standard model of cosmology includes the action of two unknown components.

Firstly, an attractive matter component, known as cold dark matter, which unlike ordinary matter does not

interact with light. Secondly, a repulsive form of energy, known as dark energy, which is driving the currently

accelerated expansion of the Universe. They have been found to be essential components to explain our

cosmos in addition to the ordinary matter we know about. But as yet we do not know what these exotic

components actually are.

Planck was launched in 2009 and collected data until 2013. Its first release – which gave rise to the almost

perfect Universe – was made in the spring of that year. It was based solely on the temperature of the cosmic

microwave background radiation, and used only the first two sky surveys from the mission.

This illustration summarizes the almost 14-billion-year long history of our Universe. It shows the main events that

occurred between the initial phase of the cosmos, where its properties were almost uniform and punctuated only by tiny

fluctuations, to the rich variety of cosmic structure that we observe today, from stars and planets to galaxies and galaxy

clusters. Copyright ESA – C. Carreau

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The data also provided further evidence for a very early phase of accelerated expansion, called inflation, in the

first tiny fraction of a second in the Universe’s history, during which the seeds of all cosmic structures were

sown. Yielding a quantitative measure of the relative distribution of these primordial fluctuations, Planck

provided the best confirmation ever obtained of the inflationary scenario.

Besides mapping the temperature of the cosmic microwave background across the sky with unprecedented

accuracy, Planck also measured its polarization, which indicates if light is vibrating in a preferred direction. The

polarization of the cosmic microwave background carries an imprint of the last interaction between the

radiation and matter particles in the early Universe, and as such contains additional, all-important information

about the history of the cosmos. But it could also contain information about the very first instants of our

Universe, and give us clues to understand its birth.

In 2015, a second data release folded together all data collected by the mission, which amounted to eight sky

surveys. It gave temperature and polarization but came with a caution.

“We felt the quality of some of the polarization data was not good enough to be used for cosmology,” says

Jan. He adds that – of course – it didn’t prevent them from doing cosmology with it but that some conclusions

drawn at that time needed further confirmation and should therefore be treated with caution.

And that’s the big change for this 2018 Legacy data release. The Planck consortium has completed a new

processing of the data. Most of the early signs that called for caution have disappeared. The scientists are now

certain that both temperature and polarization are accurately determined.

“Now we really are confident that we can retrieve a cosmological model based on solely on temperature, solely

on polarization, and based on both temperature and polarization. And they all match,” says Reno Mandolesi,

principal investigator of the LFI instrument on Planck at the University of Ferrara, Italy.

“Since 2015, more astrophysical data has been gathered by other experiments, and new cosmological

analyses have also been performed, combining observations of the CMB at small scales with those of galaxies,

clusters of galaxies, and supernovae, which most of the time improved the consistency with Planck data and

the cosmological model supported by Planck,” says Jean-Loup Puget, principal investigator of the HFI

instrument on Planck at the Institut d'Astrophysique Spatiale in Orsay, France.

This is an impressive feat and means that cosmologists can be assured that their description of the Universe as

a place containing ordinary matter, cold dark matter and dark energy, populated by structures that had been

seeded during an early phase of inflationary expansion, is largely correct.

But there are some oddities that need explaining – or tensions as cosmologists call them. One in particular is

related to the expansion of the Universe. The rate of this expansion is given by the so-called Hubble Constant.

To measure the Hubble constant astronomers have traditionally relied on gauging distances across the

cosmos. They can only do this for the relatively local Universe by measuring the apparent brightness of certain

types of nearby variable stars and exploding stars, whose actual brightness can be estimated independently. It

is a well-honed technique that has been developed over the course of the last century, pioneered by Henrietta

Leavitt and later applied, in the late 1920s, by Edwin Hubble and collaborators, who used variable stars in

distant galaxies and other observations to reveal that the Universe was expanding.

The figure astronomers derive for the Hubble Constant using a wide variety of cutting-edge observations,

including some from Hubble’s namesake observatory, the NASA/ESA Hubble Space Telescope, and most

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recently from ESA’s Gaia mission, is 73.5 km/s/Mpc, with an uncertainty of only two percent. The slightly

esoteric units give the velocity of the expansion in km/s for every million parsecs (Mpc) of separation in space,

where a parsec is equivalent to 3.26 light-years.

A second way to estimate the Hubble Constant is to use the cosmological model that fits the cosmic

microwave background image, which represents the very young Universe, and calculate a prediction for what

the Hubble Constant should be today. When applied to Planck data, this method gives a lower value of 67.4

km/s/Mpc, with a tiny uncertainty of less than a percent.

On the one hand, it is extraordinary that two such radically different ways of deriving the Hubble constant –

one using the local, mature Universe, and one based on the distant, infant Universe – are so close to each

other. On the other hand, in principle these two figures should agree to within their respective uncertainties.

This is the tension, and the question is how can they be reconciled?

Both sides are convinced that any remaining errors in their measurement methodologies are now too small to

cause the discrepancy. So could it be that there is something slightly peculiar about our local cosmic

environment that makes the nearby measurement somewhat anomalous? We know for example that our

Galaxy sits in a slightly under-dense region of the Universe, which could affect the local value of the Hubble

constant. Unfortunately, most astronomers think that such deviations are not large enough to resolve this

problem.

“There is no single, satisfactory astrophysical solution that can explain the discrepancy. So, perhaps there is

some new physics to be found,” says Marco Bersanelli, deputy principal investigator of the LFI instrument at

the University of Milan, Italy.

‘New physics’ means that exotic particles or forces could be influencing the results. Yet, as exciting as this

prospect feels, the Planck results place severe constraints on this train of thought because it fits so well with

the majority of observations.

“It is very hard to add new physics alleviating the tension and still keep the standard model’s precise

description of everything else that already fits,” says François Bouchet, deputy principal investigator of the HFI

instrument at the Institut d'Astrophysique de Paris, France.

As a result, no one has been able to come up with a satisfactory explanation for the differences between the

two measurements, and the question remains to be resolved.

“For the moment, we shouldn’t get too excited about finding new physics: it could well be that the relatively

small discrepancy can be explained by a combination of small errors and local effects. But we need to keep

improving our measurements and thinking about better ways to explain it,” says Jan.

This is the legacy of Planck: with its almost perfect Universe, the mission has given researchers confirmation of

their models but with a few details to puzzle over. In other words: the best of both worlds.

Source: European Space Agency Return to Contents

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Space Image of the Week

The Extraordinary Spiral in LL Pegasi Image Credit: NASA, ESA, Hubble, HLA; Processing & Copyright: Domingo Pestana &Raul

Villaverde

Explanation: What created the strange spiral structure on the upper left? No one is sure, although it is likely

related to a star in a binary star system entering the planetary nebula phase, when its outer atmosphere is

ejected. The huge spiral spans about a third of a light year across and, winding four or five complete turns,

has a regularity that is without precedent. Given the expansion rate of the spiral gas, a new layer must appear

about every 800 years, a close match to the time it takes for the two stars to orbit each other.

The star system that created it is most commonly known as LL Pegasi, but also AFGL 3068. The unusual

structure itself has been cataloged as IRAS 23166+1655. The featured image was taken in near-infrared light

by the Hubble Space Telescope. Why the spiral glows is itself a mystery, with a leading hypothesis being

illumination by light reflected from nearby stars.

Source: NASA APOD Return to Contents