Exoplanet measured with remarkable precision

Barely 30 years ago, the only planets astronomers had found were located right here in our own solar system.

The Milky Way is chock-full of stars, millions of them similar to our own sun. Yet the tally of known worlds in other star systems was exactly zero.

What a difference a few decades can make.

As 2014 unfolds, astronomers have not only found more than a thousand "exoplanets" circling distant suns, but also they're beginning to make precise measurements of them.

The old void of ignorance about exoplanets is now being filled with data precise to the second decimal place.

A team led by Sarah Ballard, a NASA Carl Sagan Fellow at the University of Washington in Seattle, recently measured the diameter of a "super Earth" to within an accuracy of 148 miles total or about 1 percent, remarkable accuracy for an exoplanet located about 300 light years from Earth.

"It does indeed seem amazing," says Ballard. "The landscape of exoplanet research has changed to an almost unrecognizable degree since I started graduate school in 2007."

To size up the planet, named "Kepler 93 b," Ballard used data from NASA's Kepler and Spitzer Space Telescopes.

First, Kepler discovered the planet. As seen from Earth, Kepler 93 b passes directly in front of its parent star, causing the starlight to dim during the transit.

That dimming, which occurs once per orbit, is what allowed Kepler mission scientists to find the planet in the first place.

Kepler Space Telescope

Next, both Spitzer and Kepler Space Telescope recorded multiple transits at visible and infrared wavelengths.

Data from the observatories agreed: Kepler 93 b was really a planet and not some artefact of stellar variability.

Ballard then knew that by looking carefully at the light curve she could calculate the size of the planet relative to the star.

At that point, the only missing piece was the diameter of the star itself.

"The precision with which we measured the size of the planet is linked directly to our measurement of the star," says Ballard. "And we measured the star using a technique called astero-seismology."

Most people have heard of "seismology," the study of seismic waves moving through the Earth. "We can learn a lot about the structure of our planet by studying seismic waves," she says.

Asteroseismology is the same thing, except for stars: The outer layers of stars boil like water on top of a hot stove. Those convective motions create seismic waves that bounce around inside the core, causing the star to ring like an enormous bell. Kepler can detect that "ringing," which reveals itself as fluctuations in a star's brightness.

Ballard's colleague, University of Birmingham professor Bill Chaplin led the asteroseismic analysis for Kepler-93 b.

"By analyzing the seismic modes of the star, he was able to deduce its radius and mass to an accuracy of a percent," she says.

The new measurements confirm that Kepler-93 b is a "super-Earth" sized exoplanet, with a diameter about one-and-a-half times the size of our planet.

Previous measurements by the Keck Observatory in Hawaii had put Kepler-93 b's mass at about 3.8 times that of Earth.

The density of Kepler-93 b, derived from its mass and newly obtained radius, suggests the planet is very likely made of iron and rock, like Earth itself.

Although super-Earths are common in the galaxy, none exist in our solar system. That makes them tricky to study.

Ballard's team has shown, however, that it is possible to learn a lot about an exoplanet even when it is very far away.

BOSS quasars track the expanding universe with precision

An artist's conception of how BOSS uses quasars to measure the distant universe. 

Light from distant quasars is partly absorbed by intervening gas, which is imprinted with a subtle ring-like pattern of known physical scale. 

Astronomers have now measured this scale with an accuracy of two percent, precisely measuring how fast the universe was expanding when it was just 3 billion years old. 

Credit: Zosia Rostomian, Lawrence Berkeley National Laboratory, and Andreu Font-Ribera, BOSS Lyman-alpha team, Berkeley Lab.

The Baryon Oscillation Spectroscopic Survey (BOSS), the largest component of the third Sloan Digital Sky Survey (SDSS-III), pioneered the use of quasars to map density variations in intergalactic gas at high redshifts, tracing the structure of the young universe.

BOSS charts the history of the universe's expansion in order to illuminate the nature of dark energy, and new measures of large-scale structure have yielded the most precise measurement of expansion since galaxies first formed.

The latest quasar results combine two separate analytical techniques. A new kind of analysis, led by physicist Andreu Font-Ribera of the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) and his team, was published late last year.

Analysis using a tested approach, but with far more data than before, has just been published by Timothée Delubac, of EPFL Switzerland and France's Centre de Saclay, and his team.

The two analyses together establish the expansion rate at 68 kilometers per second per million light years at redshift 2.34, with an unprecedented accuracy of 2.2 percent.

"This means if we look back to the universe when it was less than a quarter of its present age, we'd see that a pair of galaxies separated by a million light years would be drifting apart at a velocity of 68 kilometers a second as the universe expands," says Font-Ribera, a postdoctoral fellow in Berkeley Lab's Physics Division.

"The uncertainty is plus or minus only a kilometer and a half per second." Font-Ribera presented the findings at the April 2014 meeting of the American Physical Society in Savannah, GA.

BOSS employs both galaxies and distant quasars to measure baryon acoustic oscillations (BAO), a signature imprint in the way matter is distributed, resulting from conditions in the early universe.

While also present in the distribution of invisible dark matter, the imprint is evident in the distribution of ordinary matter, including galaxies, quasars, and intergalactic hydrogen.

"Three years ago BOSS used 14,000 quasars to demonstrate we could make the biggest 3-D maps of the universe," says Berkeley Lab's David Schlegel, principal investigator of BOSS.

"Two years ago, with 48,000 quasars, we first detected baryon acoustic oscillations in these maps. Now, with more than 150,000 quasars, we've made extremely precise measures of BAO."

The BAO imprint corresponds to an excess of about five percent in the clustering of matter at a separation known as the BAO scale.

Recent experiments including BOSS and ESA's Planck satellite study of the cosmic microwave background put the BAO scale, as measured in today's universe, at very close to 450 million light years, a "standard ruler" for measuring expansion.

BAO directly descends from pressure waves (sound waves) moving through the early universe, when particles of light and matter were inextricably entangled; 380,000 years after the big bang, the universe had cooled enough for light to go free.

The cosmic microwave background radiation preserves a record of the early acoustic density peaks; these were the seeds of the subsequent BAO imprint on the distribution of matter.

More information: "Quasar-Lyman α Forest Cross-Correlation from BOSS DR11: Baryon Acoustic Oscillations," by Andreu Font-Ribera, et al., has been submitted to the Journal of Cosmology and Astropartical Physics and is now available online at arxiv.org/abs/1311.1767.

JILA strontium atomic clock sets new records in both precision and stability

JILA's experimental atomic clock based on strontium atoms held in a lattice of laser light is the world's most precise and stable atomic clock. 

The image is a composite of many photos taken with long exposure times and other techniques to make the lasers more visible. 

Credit: Ye group and Baxley/JILA

Heralding a new age of terrific timekeeping, a research group led by a National Institute of Standards and Technology (NIST) physicist has unveiled an experimental strontium atomic clock that has set new world records for both precision and stability— key metrics for the performance of a clock.

The clock is in a laboratory at JILA, a joint institute of NIST and the University of Colorado Boulder.

Described in a new paper in Nature, the JILA strontium lattice clock is about 50 percent more precise than the record holder of the past few years, NIST's quantum logic clock.

Precision refers to how closely the clock approaches the true resonant frequency at which its reference atoms oscillate between two electronic energy levels.

The new strontium clock is so precise it would neither gain nor lose one second in about 5 billion years, if it could operate that long. (This time period is longer than the age of the Earth, an estimated 4.5 billion years old.)

The strontium clock's stability—the extent to which each tick matches the duration of every other tick—is about the same as NIST's ytterbium atomic clock, another world leader in stability unveiled in August, 2013.

Stability determines in part how long an atomic clock must run to achieve its best performance through continual averaging.

The strontium and ytterbium lattice clocks are so stable that in just a few seconds of averaging they outperform other types of atomic clocks that have been averaged for hours or days.

"We already have plans to push the performance even more," NIST/JILA Fellow and group leader Jun Ye says.

"So in this sense, even this new Nature paper represents only a 'mid-term' report. You can expect more new breakthroughs in our clocks in the next 5 to 10 years."

The current international definition of units of time requires the use of cesium-based atomic clocks, such as the current U.S. civilian time standard clock, the NIST-F1 cesium fountain clock.

Hence only cesium clocks are accurate by definition, even though the strontium clock has better precision.

The strontium lattice clock and some other experimental clocks operate at optical frequencies, much higher than the microwave frequencies used in cesium clocks.

Thanks to the work at NIST, JILA and other research organizations across the world, the strontium lattice clock and other experimental clocks may someday be chosen as new timekeeping standards by the international community.

The strontium clock is the first to hold world records for both precision and stability since the 1990s, when cesium fountain atomic clocks were introduced.

In the past decade, the rapid advances in experimental atomic clocks at NIST and other laboratories around the world have surprised even some of the scientists leading the research.

NIST, which operates the NIST-F1 time standard, pursues multiple clock technologies because scientific research can take unpredictable turns, and because different types of atomic clocks are better suited for different practical applications.

In JILA's world-leading clock, a few thousand atoms of strontium are held in a column of about 100 pancake-shaped traps called an optical lattice formed by intense laser light.

JILA scientists detect strontium's "ticks" (430 trillion per second) by bathing the atoms in very stable red laser light at the exact frequency that prompts the switch between energy levels.

More information: B.J. Bloom, T.L. Nicholson, J.R. Williams, S.L. Campbell, M. Bishof, X. Zhang, W. Zhang, S.L. Bromley and J. Ye. A new generation of atomic clocks: Total uncertainty and instability at the 1018 level. Nature. Posted online Jan. 22, 2014. DOI: 10.1038/nature12941

NASA-NOAA Suomi NPP VIIRS satellite sensor: More precise hurricane forecasts

Tropical Storm Flossie imagery in July 2013 from Suomi NPP’s VIIRS Day-Night band revealing that the storm shifted more to the north, sparing the big island of Hawaii from a direct hit, but bringing the islands of Oahu, Molokai and Maui into a tropical storm warning area. 

Credit: NOAA

The ability to use satellites to locate a storm that could evolve into a severe storm or hurricane will likely become more accurate for this year's Atlantic hurricane season beginning June 1.

By then, the National Oceanic and Atmospheric Administration's (NOAA), weather forecasters will be able to further improve the use of sensors aboard the NASA-NOAA Suomi National Polar-orbiting Partnership satellite (Suomi NPP).

U.S. Polar Environmental satellites such as Suomi NPP provide complete global coverage twice daily, while NOAA/NASA Geostationary Operational Environmental Satellites offer imagery over a fixed area.

To improve the ability to better find and track hurricanes, NOAA scientists are finding ways to incorporate data from Suomi NPP's Visible Infrared Imaging Radiometer Suite, VIIRS sensor, that allows observations of Earth's atmosphere and surface during nighttime hours and offers enhanced capability to see through clouds.

VIIRS provides many advances over previous operational imagers and advances compared to its research predecessor, the Moderate Resolution Imaging Spectroradiometers (MODIS) currently operating on NASA's Aqua and Terra satellites.

It is these advances in polar imagery that will give forecasters a new tool to improve their predictions.

Similarly, the radar on board the NASA/Japan Aerospace Exploration Agency Tropical Rainfall Measuring Mission (TRMM) satellite has the capability to see through and distinguish between precipitating cumulus and the cirrus clouds which TRMM's infrared sensor also detects.

The next-generation of these sensors is set to launch from Japan next month aboard the Global Precipitation Measurement (GPM) satellite.

The information to track storms comes from satellites surface stations, weather balloons, radar and aircraft.

Most current satellites provide important information during day and night, although observations in the visible part of the spectrum are limited at night.

That is where VIIRS has an advantage. The VIIRS day-night band is sensitive enough to provide storm information even under limited moonlight conditions, a major advancement for storm analysis.

The Advanced Technology Microwave Sounder (ATMS) sensor aboard Suomi NPP also provides temperature and water vapour measurements with greater accuracy than similar microwave instruments onboard earlier satellites.

In relatively clear areas away from the storm center and in the eye of intense storms, the Cross-track Infrared Sensor (CrIS), also on Suomi NPP, enhances ATMS temperature and moisture information by providing measurements with even greater vertical and horizontal resolution.

Installation of the CrIS instrument. Credit: Ball Aerospace