When the solar wind dies down, an outer layer of Venus's atmosphere billows outward, making the second planet from the sun look like a comet.
Image: ESA/Wei et al.
The planet Venus sometimes looks less like a planet and more like a comet, scientists say.
Scientists with the European Space Agency have discovered that a part of the upper atmosphere of Venus — its ionosphere — acts surprisingly different depending on daily changes in the sun's weather. The side of Venus' ionosphere that faces away from the sun can billow outward like the tail of a comet, while the side facing the star remains tightly compacted, researchers said.
The discovery was made using ESA's Venus Express spacecraft, which observed Venus's ionosphere during a period of low solar wind in 2010 to see exactly how the sun affects the way the planet's atmosphere functions. In 2013, the sun is expected to reach the peak of its 11-year solar activity cycle.
"As this significantly reduced solar wind hit Venus, Venus Express saw the planet’s ionosphere balloon outwards on the planet’s ‘downwind’ nightside, much like the shape of the ion tail seen streaming from a comet under similar conditions," ESA officials said in a statement today (Jan. 29).
It only takes 30 to 60 minutes for the planet's comet-like tail to form after the solar wind dies down. Researchers observed the ionosphere stretch to at least 7,521 miles (12,104 kilometers) from the planet, said Yong Wei, a scientist at the Max Planck Institute in Katlenburg, Germany who worked on this research.
Earth's ionosphere never becomes comet-like largely because the planet has its own magnetic field that balances out the sun's influence on the way the atmospheric layer is shaped. Venus, however, doesn't have its own magnetic field and is therefore subject to the whims of the sun's solar wind.
Researchers think that Mars behaves in much the same way. The Red Planet doesn't have a magnetic field to mitigate the influence of the sun's wind either.
The Venus Express spacecraft launched in 2005 and has been orbiting the second planet from the sun since 2006. The spacecraft is equipped with seven instruments to study the atmosphere and surface of Venus in extreme detail. The spacecraft is currently in an extended mission slated to last until 2014.
- Amazing Venus Photos by ESA's Venus Express
- Photos: Spectacular Comet Views from Earth and Space
- Venus Express: January and June Fly-bys Snapped By Orbiter | Video
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14 Comments
Add Comment"It only takes 30 to 60 minutes for the planet's comet-like tail to form after the solar wind dies down."
Reply | Report Abuse | Link to thisAm I missing the explanation as to why the diminishment of the Solar wind produces Venus' comet-like tail? It would intuitively seem that an increase in the Solar wind would be required to distort Venus' upper atmosphere, producing the comet-like tail...
jtdwyer - That puzzles me as well.
Reply | Report Abuse | Link to thisMy question is how much of Venus' atmosphere is lost to this effect and how long it would take for the atmospheric density to lower sufficiently that our probes could survive on the surface? It would also be interesting to know what the atmospheric pressure may have been millions of years ago calculating backwards.
How rare is rare earth?
Reply | Report Abuse | Link to thisA magnetic field is unlikely to be an absolute necessity for life to begin and evolve, but it probably helps.
More and more planets in distant solar systems are being discovered, but how many of them have a magnetic field?
BillR - That is an interesting thought. My guess would be that, since it's the upper atmosphere that's mentioned as the source of he tail, the dense lower atmosphere is not affected and would still present an obstacle to probe survival. However, it's difficult to rely on anything the article says unless the anomalous inverse solar wind effect is better explained...
Reply | Report Abuse | Link to thisYep, complex life certainly can't evolve unless it can reliably replicate... That's how microbial life on moons covered by water ice might develop, shielded from cosmic rays by the dense ice. It would be most important to understand which of the many exoplanets being discovered have radiation sufficient to provide energy, water to provide motility and a gravitational field to provide shelter from highly energetic particles. However, as I understand those properties are very difficult to ascertain...
Reply | Report Abuse | Link to thisSolar wind transforms Venus into a giant electrified avocado.
Reply | Report Abuse | Link to thisPoorly written piece. Why the inverse relationship between solar wind and atmospheric drag? Please explain! And the associated videoclip -- what was that supposed to show, except perhaps that it's a cloudy day on Venus?
Reply | Report Abuse | Link to thisSome interesting discussion here might shed some more light on it.
Reply | Report Abuse | Link to thishttp://www.sott.net/article/257308-Venus-behaves-like-comet-during-reduced-solar-wind-pressure
I really should thank Carlyle very much for identifying the source of my confusion, and restore his link to the clarifying definitive news release on the subject:
Reply | Report Abuse | Link to thishttp://www.esa.int/Our_Activities/Space_Science/When_a_planet_behaves_like_a_comet
Its key points include:
"The ionosphere is a region of weakly electrically charged gas high above the main body of a planet’s atmosphere. Its shape and density are partly controlled by the internal magnetic field of the planet."
"For Earth, which has a strong magnetic field, the ionosphere is relatively stable under a range of solar wind conditions. By comparison, Venus does not have its own internal magnetic field and relies instead on interactions with the solar wind to shape its ionosphere."
"As this significantly reduced solar wind hit Venus, Venus Express saw the planet’s ionosphere balloon outwards on the planet’s ‘downwind’ nightside, much like the shape of the ion tail seen streaming from a comet under similar conditions."
As I understand, the Earth's magnetic field primarily generates the ionized plasma of its ionosphere and maintains its stability even as the Solar wind varies. Venus's ionosphere is produces solely by its gaseous atmosphere's interaction with the Solar wind: the magnitude of its charge is produced by its accumulated effects. When the Solar wind suddenly diminishes, the relative pressure of Venus' ionospheric plasma's charge flow increases, causing it to expand.
If I understand correctly, while the pressure of the Solar wind that causes the tail to form, a decrease in its pressure causes the pressure induced by Venus' ionosphere causes it to expand....
Thanks again, Carlyle!
The new observations settle a debate about how the strength of the solar wind affects the way in which ionospheric plasma is transported from the dayside to the nightside of Venus.
Reply | Report Abuse | Link to thisUsually, this material flows along a thin channel in the ionosphere, but scientists were unsure what happens under low solar wind conditions. Does the flow of plasma particles increase as the channel widens due to the reduced confining pressure, or does it decrease because less force is available to push plasma through the channel?
“We now finally know that the first effect outweighs the second, and that the ionosphere expands significantly during low solar wind density conditions,” says Markus Fraenz, also of the Max Planck Institute and co-author on the paper.
http://www.esa.int/Our_Activities/Space_Science/When_a_planet_behaves_like_a_comet
I posted this clearer explanation together with a criticism of SA for not including it in the first place. My post was deleated.
jtdwyer said, "As I understand, the Earth's magnetic field primarily generates the ionized plasma of its ionosphere and maintains its stability even as the Solar wind varies. Venus's ionosphere is produces solely by its gaseous atmosphere's interaction with the Solar wind: the magnitude of its charge is produced by its accumulated effects."
Reply | Report Abuse | Link to thisMy understanding of the ionosphere is that the "ionized plasma" is "generated" by solar radiation (primarily UV) and not by the "Earth's magnetic field" or the "solar wind" in the case of Vensus.
Regarding the behavior of Venus' nightside ionosphere, there are some excellent diagrams in the Wei, et. al. paper:
http://www.sciencedirect.com/science/article/pii/S0032063312002619
This summary at ESA might offer addition insight:
http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=51315
OK - well, I had to rewrite my original comment, too!
Reply | Report Abuse | Link to thisSo, I misstated that the Earth's ionosphere is produced by the Earth's magnetic field. I should have said that the Earth's magnetic field primarily determines the shape of the ionosphere (generally, the inner portion of the magnetosphere), while the Solar wind determines the shape of Venus' ionosphere. The previously referenced ESA report states:
"For Earth, which has a strong magnetic field, the ionosphere is relatively stable under a range of solar wind conditions. By comparison, Venus does not have its own internal magnetic field and relies instead on interactions with the solar wind to shape its ionosphere."
http://www.esa.int/Our_Activities/Space_Science/When_a_planet_behaves_like_a_comet
Cramer said:
"My understanding of the ionosphere is that the "ionized plasma" is "generated" by solar radiation (primarily UV) and not by the "Earth's magnetic field" or the "solar wind" in the case of Vensus." (why all the dismissive quotes?)
The ionization of particles in the ionosphere (thus producing the ionosphere) is mostly a result of atmospheric interaction with UV radiation as you say, but also x-rays and protons and other charged particles that constitute the Solar wind.
Some supporting references:
"The solar wind creates the heliosphere, ... and the plasma tails of comets that always point away from the Sun."
http://en.wikipedia.org/wiki/Solar_wind
The additional ESA report you referenced also attributes the ionization of Venus' atmosphere to the "Solar wind":
"The results also show that erosion of the planet's upper atmosphere by the solar wind ceases when the wind nearly disappears, but may be enhanced in the aftermath of such a period. A large "bubble" of slow-moving ions is formed behind the planet and when pressure increases again this bubble will partly be lost into space, temporarily accelerating the rate of erosion again."
The Wei, et al. research report abstract states:
"We interpret this low-speed O+ as a constituent of the extended nightside ionosphere as a consequence of long-duration (18 h) tenuous solar wind, because the very low dynamic pressure enhances the source and reduces the sink of the nightside ionosphere."
I think this is consistent with the summary explanation I provided earlier:
"If I understand correctly, while the pressure of the Solar wind that causes the tail to form, a decrease in its pressure causes the pressure induced by Venus' ionosphere causes it to expand..."
Unfortunately, I can't refer to the statements in my original comment. Thanks for your personal assessments, but they reveal more about yourself than me.
Reply | Report Abuse | Link to thisJtDwyer, you are wrong again. I never replied to your deleted statement. I replied to your statement that is still there. Here is what you said:
Reply | Report Abuse | Link to this"As I understand, the Earth's magnetic field primarily generates the ionized plasma of its ionosphere and maintains its stability even as the Solar wind varies. Venus's ionosphere is produces solely by its gaseous atmosphere's interaction with the Solar wind: the magnitude of its charge is produced by its accumulated effects."
When you speak of "the ionized plasma of its ionsphere," it is very clear what you meant.
A google search of SciAm for jtdwyer gives 4,560 hits. I have read many of your comments. You constantly get the science wrong. When someone corrects you, you then resort to semantical arguments, red herrings, and ad hominems.
Your last comment was an ad hominem. I have only critized your comments (i.e. your behavior). I have never made personal attacks on you. That is, I have never questioned your intelligence, your chararacter, your personality, your motives, etc.