The End of Cassini

September 15, 2017
After twenty years of studying the planet Saturn, the working life of the Cassini spacecraft will come to an end in the next few hours. On Friday, September 15, 2017 at about 7:55 am EDT, NASA will crash the probe into the surface of Saturn and end its mission.

As far back as the 1980s astronomers from around the world were making plans to send a probe to the gas giant, Saturn. We had already explored both Mars and Venus, and the Voyager probes had made flybys of the outer planets, but Saturn was still not well explored. Eventually a cooperative project involving NASA in the United States, ESA in Europe, and ASI in Italy was developed to launch an orbiter to Saturn.

Finally on October 15, 1997 a Titan rocket lifted the Cassini probe into space. It spent the next seven years traveling through the solar system before entering a stable orbit on July 1, 2004. 

One amazing aspect of the Cassini mission has been its unexpected longevity. The initial mission was planned for 2004 to 2008, a meagre four years of orbiting Saturn and taking various measurements from orbit. At the end of its initial mission, it was still operating and so the mission was extended another two years. When the second mission ended, the Cassini probe was still in good shape and so a third mission was initiated which would last seven more years, and would include further exploration of the moons of Saturn.

Unfortunately the probe is now reaching the end of its usable life. Although it is in a stable orbit, crews on Earth still need to send commands for it to correct its position and adjust its orientation, and each such movement uses a small amount of fuel. And that fuel supply is now nearly exhausted. The crews could allow the probe to continue in orbit and continue collecting data, but that is a risky choice. At some point the probe will no longer be able to have its orbit adjusted, and will crash into either Saturn or one of its moons.

And that is the big concern that led to the decision to crash Cassini intentionally. Two of these moons, Titan and Enceladus, have interesting geographies and chemical compositions, and may even harbor some form of microbial life. If the Cassini probe collides with either of them, it could contaminate their surfaces or otherwise damage them. An uncontrolled crash by Cassini into one of the moons could cause far more scientific harm than any benefit that we would garner by allowing the mission to continue. 

And so for those reasons, the decision was made to order Cassini to fly into the surface of Saturn. Hopefully it will be transmitting data during its descent, and will provide more data on the atmosphere of the gas giant. Whatever happens, this little probe that has lasted three times its expected lifespan will have provided more data to astronomers and scientists than we would have ever thought possible when it was first launched. It has been a very successful mission, and will no doubt lead to more great discoveries in the future!

Those wishing to view the final descent of Cassini can do so here.
 

The HL-LHC

September 14, 2017
As students around the world return to school, or start college, or begin new coursework and training of other kinds, particle physicists are also starting new things in the form of new data runs from the Large Hadron Collider. The LHC has already produced evidence of the Higgs boson, and added further constraints to many other theories of nature. The next data run could easily find evidence of dark matter, dark energy, or even hidden higher dimensions in the Universe.

However the topic of tod...
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Back To School

September 5, 2017

Some loyal readers will recognize this entry as a repeat from the last three years. Each year it gets a good response, and kudos from my readers, and so as before I must appease my loyal followers...

To all the students starting University, enjoy this time of your life. Long ago when I started, a prof told me that this is the start of your real education. Now you get to choose your own courses and your own field of study. It is entirely up to you to decide what to do with this chance.

I know fr...


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Free Software

September 5, 2017
With the arrival of September, students around the world will be returning to classes this week. And for those who are starting out at college or university, one of the most important considerations is how to live on a budget. These are the years when one has little or no income, but must bear the expenses of living independently for the first time. While giving advice on living on a budget is far too expansive to cover in this blog, I can tackle one small aspect of student life by providing ...
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The Antihydrogen Spectrum

August 3, 2017
Another interesting result from the Canadian led team at the ALPHA collaboration, with a paper publish today in Nature in which they present the hyperfine spectrum of anti-hydrogen.

Anyone who has the least interest in either physics or astronomy is aware of atomic spectra. Over a century ago scientists discovered that each chemical element emits a signature series of wavelengths of light, which is unique to that element. From the colour of emitted light we can identify each element that is p...
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Ten Years of GalaxyZoo

July 11, 2017
Happy 10th Anniversary to the team behind the GalaxyZoo website!

Back in 2007 a group of astronomers set up this program that would provide images from professional telescopes to the public, and allow dedicated volunteers to classify the different types of galaxies that were visible. This has produced countless academic papers in peer reviewed journals, and has allowed an army of amateur scientists to have a real impact on our understanding of the Universe.

On a personal level, I was a graduate...
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Simpson's Paradox Visualized

July 10, 2017
A while ago I wrote an article about an interesting statistical phenomenon known as Simpson's Paradox. According to Simpson's Paradox, a company can have discriminatory hiring policies in spite of each of its individual departments being completely fair. A new medical treatment can work better than existing methods for both the young and the old, and yet it gives worse results when you don't know the age of the patient. And it can make a single data set produce opposite and contradictory resu...
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A Forty Year Old Mystery Is Solved

June 7, 2017
After forty years of speculations ranging from exotic particle decays to advanced alien civilizations, the famous 6EQUJ5 signal has now been explained, and the explanation is embarrassingly rather basic.

In August 1977, astronomers at the Big Ear observatory at Ohio State university were scanning the sky for radio signals from space. There are numerous sources of radio waves in the galaxy, and a lot of interesting science can be done using a map of the sources of radio signals. And of course m...
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X-Ray Navigation & Communication

June 1, 2017
Yesterday I wrote about the theory of neutron stars and pulsars, and about the NICER mission that is about to begin examining them in more detail. After fifty years of theoretical study and limited astronomical data, we are soon to have a dedicated x-ray telescope with the primary purpose of studying the composition and properties of pulsars in the galaxy.

However the mission has a second goal, and one with a more practical purpose than studying distant neutron stars and pulsars. The mission w...
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A NICER Mission

June 1, 2017
Nearly fifty years ago, astronomers discovered a bizarre signal in the sky coming from an unknown, mysterious object. Where most astrophysical objects send a steady stream of particles, light and radio waves, this new object was rapidly pulsing x-rays. 

These objects were eventually found to be very compact objects, known as neutron stars. When a star reaches the end of its life, and has exhausted its supply of nuclear fuel, it will expel its outer layers and the core will collapse into a smal...
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About Me


Dr. Chris Bird I am a theoretical physicist & mathematician, with training in electronics, programming, robotics, and a number of other related fields.

   


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