Posts tagged astronomers
CU Boulder’s sun-gazing SORCE satellite, designed to last 5 years, turns 10
Jan 22nd
A decade later, the four instruments onboard the Solar Radiation and Climate Experiment, or SORCE, have given scientists an unprecedented look at some of the most intense solar eruptions ever witnessed — including the notorious Halloween storms in October and November 2003 — as well as the anomalously quiet solar minimum that hushed the sun’s surface beginning in 2008 and, now, a new solar maximum that appears to be the least active in a century.
“We were there to see it transform from a fairly normal solar cycle to a very low-activity solar cycle,” said Tom Woods, associate director of CU-Boulder’s Laboratory for Atmospheric and Space Physics, known as LASP, and principal investigator for SORCE. “Of course we couldn’t predict or know that, but it’s very exciting.”
The data generated by SORCE’s instruments, which were originally designed to operate for just five years, are downloaded twice a day with the help of CU-Boulder undergraduates working at LASP mission control. Scientists are now using that data to better understand how energy from the sun affects Earth’s climate. While human-produced greenhouse gases have been the dominant driver of climate change over the last several decades, the activity of the sun can either enhance or offset the resulting global warming.
“About 10 to 15 percent of the climate warming since 1970 is due to the sun,” Woods said. “That’s going to change now. Now that solar activity is low, the global warming trend could slow down some, but not nearly enough to offset the anthropogenic effects on global warming.”
The current, lackluster solar maximum is being compared to periods when astronomers observed very few sunspots in the early 19th century known as the Dalton Minimum and in the last half of the 17th century known as the Maunder Minimum. During the Maunder Minimum, which coincided with an era known as the Little Ice Age, temperatures in Europe were especially cool, with rivers and canals freezing during the winter across the continent and rapidly advancing glaciers destroying villages in the Swiss Alps.
The SORCE mission is also a critical contributor to the long-term record of total solar irradiance — the magnitude of the sun’s energy when it reaches the top of the Earth’s atmosphere — which stretches back to 1978, when the Nimbus-7 satellite was launched. The Total Irradiance Monitor, or TIM, instrument onboard SORCE is taking the most accurate and most precise measurements of total solar irradiance ever collected.
“The total solar irradiance provides nearly all the energy powering the Earth’s climate system, exceeding all other energy sources combined by 2,500 times,” said Greg Kopp, LASP senior research scientist and co-investigator responsible for the TIM instrument. “Any change in total irradiance can thus have large effects on our climate.”
Data from the SORCE mission have also begun a new record for measurements of visible and near-infrared light emitted from the sun. The solar spectral irradiance measurements are being made for the first time by the Spectral Irradiance Monitor, or SIM. Combined with other instruments onboard SORCE, scientists can now see all the wavelengths, including those in the ultraviolet range, emitted by the sun at once. This new way of seeing the sun has led to interesting discoveries, including that the energy emitted in some wavelengths of light vary out of phase with the sun’s overall activity, actually increasing as the number of sunspots decreases.
Now that SORCE has doubled its original life expectancy, LASP scientists are building new instruments to take over when SORCE gives out. A new TIM built at LASP launched on NASA’s Glory mission in 2011, but the satellite failed to make orbit. After the loss of Glory, CU-Boulder scientists, determined to avoid a gap in the record of total solar irradiance measurements, came up with a creative solution, repurposing a ground-based TIM to quickly make it space-worthy and then integrating it onto a U.S. Air Force satellite built by Ball Aerospace that is set to launch in August of this year.
“It’s important to have continuous measurements of solar irradiance since we’re looking for small changes in the sun’s output over decades and even centuries,” said Kopp. “Detecting such small changes using measurements disconnected in time would make this even more difficult.”
A new SIM instrument, also built at LASP, is scheduled to launch in 2016 on a National Oceanic and Atmospheric Administration satellite. But while SORCE is expected to continue functioning for at least another year, allowing for overlapping measurements with the TIM instrument launching in August, it’s uncertain if SORCE’s SIM instrument will still be running when its successor makes it to space in 2016.
“We’re definitely hoping and planning that SORCE lasts through this year,” Woods said. “But 2016 — I don’t think SORCE’s battery is going to last that long.”
During SORCE’s 10-year foray in space, the satellite also witnessed two rare transits of the planet Venus in front of the sun and another two less-infrequent transits by Mercury. When Venus, the larger of the two planets and the closer to Earth, blocked out part of the sun’s light, SORCE’s TIM instrument measured a corresponding drop in the amount of total solar irradiance. The measurements are now useful reference tools for astronomers hoping to discover planets around other stars by measuring a dip in a star’s light from a planetary transit.
In all, CU-Boulder has received about $120 million from NASA for the construction and operation of SORCE. But in 2008, LASP took the unusual step of returning $3 million in cost savings from the SORCE mission to NASA that resulted from the program’s efficient operations.
Researchers at LASP are planning to celebrate SORCE’s 10th birthday with cake, a science seminar and a write-up of the satellite’s top-10 accomplishments in NASA’s The Earth Observer magazine.
But while the decade mark is typically an important milestone for celebration here on Earth, the more appropriate milestone for SORCE may come in 2014 at the 11-year mark, the average length of a complete solar cycle
“Eleven years is special to us,” Woods said. “Instead of having a big science conference this year, we’re planning it for next January.”
For more information, visit LASP’s SORCE website at http://lasp.colorado.edu/sorce/index.htm.
A video of CU-Boulder researchers discussing the SORCE mission is available at http://www.colorado.edu/news/multimedia/cu-boulders-sun-gazing-satellite-turns-10-0.
CU scientists discover earlier warming period
Oct 7th
If you think global warming is bad, 11 billion years ago the entire universe underwent what might be called universal warming. The consequence of that early heating was that fierce blasts of radiation from voracious black holes stunted the growth of some small galaxies for a stretch of 500 million years.
That is the conclusion of a team of astronomers led by the University of Colorado at Boulder who used the new capabilities of NASA’s Hubble Space Telescope to probe the invisible, remote universe.
Using the newly installed Cosmic Origins Spectrograph, or COS, the team identified an era from 11.7 to 11.3 billion years ago when the universe stripped electrons off from primeval helium atoms — a process called ionization. This process heated intergalactic gas and inhibited it from gravitationally collapsing to form new generations of stars in some small galaxies. The lowest-mass galaxies were not even able to hold onto their gas, and it escaped back into intergalactic space.
CU-Boulder Professor Michael Shull of the astrophysical and planetary sciences department and his team were able to find the telltale helium spectral absorption lines in the ultraviolet light from a quasar — the brilliant core of an active galaxy. The quasar beacon shines light through intervening clouds of otherwise invisible gas, like a headlight shining through a fog. The beam allows for a core-sample probe of the clouds of gas interspersed between galaxies in the early universe.
The universe went through an initial heat wave over 13 billion years ago when energy from early massive stars ionized cold interstellar hydrogen from the Big Bang. This time period is called the Reionization Epoch because the hydrogen nuclei were originally in an ionized state shortly after the Big Bang, said Shull, also a faculty member at CU-Boulder’s Center for Astrophysics and Space Astronomy, or CASA.
A paper on the subject will be published in the Oct. 20 issue of The Astrophysical Journal. Co-authors included CASA Research Associate Kevin France, CASA Research Associate Charles Danforth, CASA postdoctoral researcher Britton Smith and Jason Tumlinson of the Space Telescope Science Institute in Baltimore.
But the Hubble data indicated it would take another 2 billion years before the universe produced sources of ultraviolet radiation with enough energy to do the heavy lifting and reionize the primeval helium that also was cooked up in the Big Bang.
This radiation didn’t come from stars, but rather from quasars, said Shull. In fact, the epoch when the helium was being reionized corresponds to a transitory time in the universe’s history when quasars were most abundant.
The universe was a rambunctious place back then, Shull said. Galaxies frequently collided and this engorged supermassive black holes in the cores of galaxies with gas falling in. The black holes furiously converted some of the gravitational energy of this mass to powerful far-ultraviolet radiation that would blaze out of galaxies. This heated the intergalactic helium from 18,000 degrees Fahrenheit to nearly 40,000 degrees.
After the helium was reionized in the universe, intergalactic gas again cooled down and dwarf galaxies could resume normal assembly. “I imagine quite a few more dwarf galaxies may have formed if helium reionization had not taken place,” said Shull.
So far Shull and his team only have one sightline from Hubble to measure the helium transition, but the COS science team plans to use Hubble to look in other directions to see if the helium reionization uniformly took place across the universe.
The $70 million COS instrument, inserted during the final Hubble servicing mission in May 2009 was designed by a team from CU-Boulder led by Professor James Green and was built primarily by Ball Aerospace & Technology Corp. of Boulder.
SOURCE: CU-BOULDER MEDIA RELEASE
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