What’s it like to see auroras on other planets? — The Conversation Article

What’s it like to see auroras on other planets?

Nathan Case, Lancaster University

Witnessing an aurora first-hand is a truly awe-inspiring experience. The natural beauty of the northern or southern lights captures the public imagination unlike any other aspect of space weather. But auroras aren’t unique to Earth and can be seen on several other planets in our solar system.

An aurora is the impressive end result of a series of events that starts at the sun. The sun constantly emits a stream of charged particles known as the solar wind into the depths of the solar system. When these particles reach a planet, such as Earth, they interact with the magnetic field surrounding it (the magnetosphere), compressing the field into a teardrop shape and transferring energy to it.

Because of the way the lines of a magnetic field can change, the charged particles inside the magnetosphere can then be accelerated into the upper atmosphere. Here they collide with molecules such as nitrogen and oxygen, giving off energy in the form of light. This creates a ribbon of colour that can be seen across the sky close to the planet’s magnetic north and south poles – this is the aurora.

Gas giant auroras

Using measurements from spacecraft, such as Cassini, or images from telescopes, such as the Hubble Space Telescope, space physicists have been able to verify that some of our closest neighbours have their own auroras. Scientists do this by studying the electromagnetic radiation received from the planets, and certain wavelength emissions are good indicators of the presence of auroras.

Each of the gas giants (Jupiter, Saturn, Uranus, and Neptune) has a strong magnetic field, a dense atmosphere and, as a result, its own aurora. The exact nature of these auroras is slightly different from Earth’s, since their atmospheres and magnetospheres are different. The colours, for example, depend on the gases in the planet’s atmosphere. But the fundamental idea behind the auroras is the same.

Blue aurora on Jupiter.
NASA/J Clarke

For example, several of Jupiter’s moons, including Io, Ganymede and Europa, affect the blue aurora created by the solar wind. Io, which is just a little larger than our own moon, is volcanic and spews out vast amounts of charged particles into Jupiter’s magnetosphere, producing large electrical currents and bright ultraviolet (UV) aurora.

On Saturn, the strongest auroras are in the UV and infrared bands of the colour spectrum and so would not be visible to the human eye. But weaker (and rarer) pink and purple auroras have also been spotted.

Hubble Space Telescope captures Saturn’s aurora.
NASA/ESA/Hubble

Mercury also has a magnetosphere and so we might expect aurora there too. Unfortunately, Mercury is too small and too close to the sun for it to retain an atmosphere, meaning the planet doesn’t have any molecules for the solar wind to excite and that means no auroras.

The unexpected auroras

On Venus and Mars, the story is different. While neither of these planets has a large-scale magnetic field, both have an atmosphere. As the solar wind interacts with the Venusian ionosphere (the layer of the atmosphere with the most charged particles), it actually creates or induces a magnetic field. Using data from the Venus Express spacecraft, scientists found that this magnetic field stretches out away from the sun to form a “magnetotail” that redirects accelerated particles into the atmosphere and forms an aurora.

Mars’s atmosphere is too thin for a similar process to occur there, but it still has aurora created by localised magnetic fields embedded in the planet’s crust. These are the remnants of a much larger, global magnetic field that disappeared as the planet’s core cooled. Interaction between the solar wind and the Martian atmosphere generates “discrete” auroras that are confined to the regions of crustal field.

A recent discovery by the MAVEN mission showed that Mars also has much larger auroras spread across the northern hemisphere, and probably the whole planet too. This “diffuse” aurora is the result of solar energetic particles raining into the Martian atmosphere, rather than particles from the solar wind interacting with a magnetic field.

If an astronaut were to stand on the surface of Mars, they might still see an aurora but it would likely be rather faint and blue, and, unlike on Earth, not be necessarily near the planet’s poles.

Brown dwarf with red aurora.
Chuck Carter and Gregg Hallinan/Caltech

Most planets outside our solar system are too dim compared to their parent star for us to see if they have auroras. But scientists recently discovery a brown dwarf (an object bigger than a planet but not big enough to burn like a star) 18 light years from Earth that is believed to have a bright red aurora. This raises the possibility of discovering other exoplanets with atmospheres and magnetic fields that have their own auroras.

Such discoveries are exciting and beautiful, but they are also scientifically useful. Investigating auroras gives scientists tantalising clues about a planet’s magnetic and particle environment and could further our understanding of how charged particles and magnetic fields interact. This could even unlock the answers to other physics problems, such as nuclear fusion.

The Conversation

Nathan Case, Senior Research Associate in Space and Planetary Physics, Lancaster University

This article was originally published on The Conversation. Read the original article.

Newsweek article

Connor Gaffey from Newsweek.com today published an article about last night’s spectacular auroral display that was visible from across the UK. Connor spoke with Nathan about how best to see the aurora in the UK and why the display last night was so strong.

Newsweek spoke to Nathan Case, a member of the Aurora Watch U.K. team at Lancaster University, who track geomagnetic activity around the British Isles and sends alerts to users when sightings of the Northern Lights are possible, to find out the best way to see the lights.

Click here to read the full article.

Nathan receives NASA Peer Award

On August 25, 2015 Nathan received the NASA Heliophysics Peer Award. The award was presented to Nathan in recognition and appreciation of superior performance of a special act, service, or achievement.

Nathan was the recipient of the NASA Heliophysics Peer Award on August 25, 2015

Nathan was the recipient of the NASA Heliophysics Peer Award on August 25, 2015

The full text of the award is as follows:

Nathan is a young PhD who has undertaken an unusual postdoc project and, through his innovation, has effectively opened up the analysis of citizen science aurora data for the space science community. He has submitted three first author papers in the past year (including a published GRL) and is working on a fourth. He has also been a co-author on numerous papers and presentations. He has worked with programmers, technical writers, educators, and human-computer interactions researchers, and is universally appreciated among a very diverse team. For these reasons, Nathan Case is presented with this 2015 Heliophysics Peer Award.

Aurorasaurus: a Citizen Science Platform for Viewing and Reporting the Aurora

The article “Aurorasaurus: a Citizen Science Platform for Viewing and Reporting the Aurora” was recently accepted to the American Geophysical Union (AGU) journal Space Weather. The article, which was co-authored by Nathan, describes the Aurorasaurus citizen science project in detail, including its aims and scopes and data collection methods.

Abstract

A new, citizen science based, aurora observing and reporting platform has been developed with the primary aim of collecting auroral observations made by the general public to further improve the modeling of the aurora. In addition, the real-time ability of this platform facilitates the combination of citizen science observations with auroral oval models to improve auroral visibility nowcasting. Aurorasaurus provides easily understandable aurora information, basic gamification, and real-time location-based notification of verified aurora activity to engage citizen scientists. The Aurorasaurus project is one of only a handful of space weather citizen science projects and can provide useful results for the space weather and citizen science communities. Early results are promising with over 2,000 registered users submitting over 1,000 aurora observations and verifying over 1,700 aurora sightings posted on Twitter.

You can download the article from Lancaster University’s repository.

Featured on Twitter’s Blog

Along with the Aurorasaurus project, Nathan’s recent study on mapping aurora with Twitter was featured in Twitter’s “Twitter data for research” blog.

Twitter data can even indicate where an Aurora Borealis may be spotted helping scientists have more sightings. After an electromagnetic storm in 2011 brought a flurry of Tweets with spottings of the Northern Lights even far down in the south, NASA scientist Elizabeth MacDonald created Aurorasaurus as a way to document sightings and to verify Tweets. A team of researchers led by Nathan Case found that Twitter data not only is a great indicator for where Aurora Borealis will be published but helps identify key characteristics of the light show including color.

Read the full blog post here.

This was an “organic” find by the data team at Twitter and is great to see the article and the project get press from Twitter.

Wired.com article

Betsy Mason from Wired.com today published a story about how Aurorasaurus is using citizen science data to map the aurora. She and Nathan discussed the project via email and Nathan provided her with information about the project and an interesting new result:

“An interesting result is that, during our case study, around 60 percent of the reported sightings occurred equatorward (southward in the northern hemisphere, and northward in the southern hemisphere) of where our current best estimate predicted,” Case told me in an email.

Click here to read the whole article.

Mapping Aurora with Twitter blog post

As our users will know, we love Twitter here at Aurorasaurus. In addition to using the social media service ourselves (check out the Twitter list of Aurorasaurus Team Members here), we present aurora-related tweets for our users to verify them as aurora sightings (a process called crowdsourcing.) We then use these “verified tweets” in just the same way as the other observations reported via our website or apps, for example, by comparing their location with the modeled auroral ovals.

Read full blog post here.

LiveScience.com article

After speaking with Nathan about his recently accepted article Mapping Auroral Activity with Twitter and the Aurorasaurus project in general, Becky Oskin from LiveScience.com has posted an article called Illuminating Tweets: Northern Lights Tracked via Twitter.

Monitoring tweets about auroras can provide accurate and timely alerts of when and where auroras are visible from the ground, said lead study author Nathan Case, a space weather scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

Click on the link to head on over to read it!

Mapping Auroral Activity with Twitter

The article “Mapping Auroral Activity with Twitter” was recently accepted to the American Geophysical Union (AGU) journal Geophysical Research Letters (GRL). The study presented in the article compared the  daily number of aurora-related tweets to several measures of auroral activity and found that the two data showed strong correlation.

Abstract

Twitter is a popular, publicly-accessible, social media service that has proven useful in mapping large-scale events in real-time. In this study, for the first time, the use of Twitter as a measure of auroral activity is investigated. Peaks in the number of aurora-related tweets are found to frequently coincide with geomagnetic disturbances (detection rate of 91%). Additionally, the number of daily aurora-related tweets is found to strongly correlate with several auroral strength proxies (ravg ≈ 0.7). An examination is made of the bias for location and time of day within Twitter data, and a first order correction of these effects is presented. Overall, the results suggest that Twitter can provide both specific details about an individual aurora and accurate real-time indication of when, and even from where, an aurora is visible.

The work undertaken was a small part of the much bigger Aurorasaurus project.

St Patrick’s Day: a Success for Citizen Science

The article “Aurorasaurus and the St Patrick’s Day storm” was recently accepted for publication in the Royal Astronomical Society (RAS) journal Astronomy & Geophysics (A&G).

The recent St. Patrick’s Day geomagnetic storm provided a rare chance for the public to witness a dazzling auroral display, even from mid-latitudes. An unprecedented number of citizen scientists reported their sightings to Aurorasaurus, offering an exciting opportunity for future scientific study.

The work undertaken was a small part of the much bigger Aurorasaurus project.