This is IMHO powerful evidence for recent warm wet Mars :
'The other surprising discovery is that ice exposed at the bottom of these meteorite impact craters is so pure,' Byrne said. 'The thinking before was that ice accumulates below the surface between soil grains, so there would be a 50-50 mix of dirt and ice. We were able to figure out, given how long it took that ice to fade from view, that the mixture is about one percent dirt and 99 percent ice.'
'The ice is a relic of a more humid climate not very long ago, perhaps just several thousand years ago.'
Dr. Bryne talks about making this ice through 'frost heave,' but it sounds to me like Arcadia Planitia may have been considerably warmer during the geologically recent past.
Remember, Mars has climate cycles, they cause the sublimation and freezing of both water and Carbon Dioxide, and both water vapor and Carbon Dioxide are powerful greenhouse gases on Mars. (As is methane, which is also present in the Martian atmosphere from unknown sources.) Presumably this ice dates from an earlier part of the climate cycle, when there was higher humidity. Higher humidity implies higher pressure and temperatures. Higher pressures could put the surface above the triple point of water, so that liquid water is possible. In that case, if the temperature gets high enough, liquid water become inevitable. That would (upon the next change in the climate cycle) freeze as very pure ice.
The Europeans keep talking about sending a rover with a drill to Mars. I think we have now found a good place for it to go.
I agree - most of this is PR, which can be ignored.
To me, the interesting thing is that these layers is that they do not represent a very long history. From Laskar et al. (2002)
For the best fit between the radiance profile and the simulated insolation parameters, we obtain an average deposition rate of 0.05 cm yr-1 for the top 250 m of deposits on the ice cap of the north pole of Mars.
Now, 5 x 10^-4 meters / year means that the top 250 meters represents ~ 500,000 years, and the entire 2 km thick cap represents maybe 5 million years. This is very brief in geological time, and interestingly may be connected to the big change in obliquity thought to have occurred about 5 million years ago. (Note - our ability to predict this back before about 5 million years ago is very poor.)
So, it's likely that not that long ago Mars had no North polar cap, and presumably it comes and goes over geologic time. What happens to the water, and how much the atmosphere increases during these periods, is effectively unknown. While many of the geologists who study Mars think that nothing much has happened there for billions of years, I think that many of the dynamists would disagree.
First, you are aware that the solar output (Solar Constant) has been measured since the 1970's ? There is no need to look at distant worlds to see if it is changing - it varies around at about the 0.1 % level.
Second, I would not put any weight on observations of any body we have not observed for more than one orbit - and that includes Pluto and (for climate) Titan. These are not simple bodies.
The general cause of Pluto's warming is well known - a highly elliptical orbit, and it's near (just past) perigee, where it outgases Methane into the atmosphere. That's one of the motivations behind Pluto Express (to get there while there is still a bigger atmosphere). It is staying warm past perigee, but we have no idea if that is normal or not. Similarly, Titan is passing through the equinox (just as we are here on Earth), and that is causing seasonal change. We know that's happening; we have no idea if what we are seeing is normal or not.
Jupiter is so different from the Earth or Mars that I wouldn't use it as an analogy for anything terrestrial, good or bad. (For example, it generates more heat internally than it gets from the Sun.) Having said that, I had not heard of any warming reported there, so a link would be welcomed.
Well, I have not the slightest doubt that Nathaniel Putzig and company know all about these earlier results - but, once you get the PR people involved, they always want to say, first, confirmed, etc.
Unlike the Earth (which has a big Moon to anchor things), Mars has huge variations in insolation due to its obliquity and eccentricity cycles. These oscillations drive large variations in climate, which causes the cool layering in the Martian Polar Caps - the so called North Polar Layered Deposits. There are lots of cool pictures of these layers.
While it is true that both the Earth and Mars would exhibit climate changes if the solar luminosity changed, so far I have not heard of any evidence requiring this from Mars. Mars's internal and orbital dynamics are quite enough to keep the climate modelers busy.
While these results are cool, the obliquity cycle was confirmed in 2002, in a paper in Nature, Orbital forcing of the martian polar layered deposits by Jacques Laskar et al., They used pictures of the layering at the edge of the polar caps, not radar, but its basically the same idea, and they showed good correlation with recent obliquity cycles.
Again, it's cool to see these layers throughout the caps, but I don't think that anyone has doubted the connection with the obliquity / insolation cycles for a while.
This sounds a lot like Kudzu - another plant brought over from Japan.
From TFA "For a while, government officials encouraged the use of cogongrass as a forage crop and as a way to stem soil erosion."
We did that with Kudzu too. What's with these agricultural guys promoting alien species they clearly know nothing about ?
Although, if nothing wants to eat it, why promote it as a forage crop ? That does suggest that some animal must like it. There must be some reason why the South of Japan is not one mass of Kudzu and cogongrass.
Let's see, people post on line anonymously, claiming to be police officers, and reporting various abuses.
The police chief "thinks some could be department employees" - translation, he thinks that they are police officers, or, at least, office employees. Implication - either they are telling the truth, or for some other reason hate his guts.
"Acevedo said he and other officers in recent months have faced allegations of sexual impropriety and suggestions that they engaged in quid pro quo behavior."
Translation : he is being accused of having sex with hookers, and letting them go free in return.
As I see it, accusing someone anonymously of these things is whistleblowing. It should be investigated, but by a third party. As it stands, it appears that the police chief is merely trying to find a legal means of finding and punishing whistleblowers. (Any trial would likely amount to the whistleblower saying, "I saw you and X, Y and Z doing this" and the police chief saying "No,you are lying, and here are officers X, Y and Z all willing to testify that you are lying, too." Good luck to the whistleblower on winning that one.)
Now, in a reasonable legal system, this would result in a special prosecutor being appointed. Pardon me for doubting that this will occur in Texas. I would be glad to be proved wrong.
Uh, the title of the actual paper is "Optimal capture trajectories using multiple gravity assists." That is exactly what Galileo Jupiter did - I worked in support of that mission way back in the early 1980's (prior to launch).
Depends on your time horizon. Millions of years, no. Human time horizons, however, we can handle.
A good, modern, numerical integrator at quadruple precision can handle the Sun, planets, and hundreds of asteroids with very small numerical errors (microns over decades). Bigger errors are introduced by observational uncertainty, primarily in the masses of the asteroids. But, even with that, errors are 100's of meters over decades.
This is not new. Almost every mission going further away than Mars or Venus uses these gravity assists, and has since Mariner 10 (1974).
I really dislike the term "gravitational currents." It conveys exactly the wrong impression. The effects of 3rd bodies is almost negligable except during close approaches, so "gravitational billiards" would be much more appropriate.
The really interesting thing is that General Relativity predicts two and only two polarizations, while other theories (that cannot be distinguished from G.R. in the usual solar system tests) have more polarizations. If and when we get a good, high SNR, detection of gravitational radiation, a profound test of gravity should follow in short order.
A gravity wave will change the distance to objects at right angles to its direction of propagation. This effect is biggest when the distance to an object is order the wavelength of the wave, or longer. (Since they travel at the speed of light, the relation between wavelength and frequency is the same as for light.) Likewise, the sensitivity is biggest when the period of the wave is between the frequency of measurement and the total duration of observations. So, pulsars are sensitive to waves with periods between about a day (they are not observed continuously) and some decades (the length of data).
Some waves are sinusoidal (distant objects appear to move closer and further away periodically), while impulsive gravitational radiation can have "memory" - i.e., the distance after the burst goes by will be permanently changed.
All of the above assumes we know the correct theory of gravity, which we won't be sure about until we actually get to study them.
LIGO and Pulsars set limits (or could detect) gravitational waves in very different parts of their frequency spectra - periods of milli seconds versus periods of months. The sources are different, the detection physics is different, etc. It's certainly worth trying both.
Also, none of the existing detectors are good enough that you can say for certain that there are known or likely astrophysical sources bright enough that they should see them. You can't talk about falsifiability until you cross that threshold, which I would expect to see happen in a decade or so.
I disagree. Look at the last 30 years of unmanned Mars exploration. We have learned really precious little and at a very slow rate. I am certainly not trying to denigrate the huge amount of effort that has gone into the unmanned effort, but we have basically answered none of the questions raised by the Viking landers. The experiment of relying only on unmanned explorations has been tried, and to me it has very clearly been found wanting.
This is not entirely a matter of technology, but also of politics, but, whatever the causes, I have watched this experiment since Viking, and in my opinion it has very clearly not been a success.
I agree, but note that a Lunar elevator could be done with existing fibers, like Zylon, No need for new materials for this case (unlike the terrestrial case, where you do).
I actually disagree. You can use existing fiber. Supposed that the heavy lift capability to the Lagrange point is 100 tons. If you dedicated one flight just to lifting your cable, you could build an elevator capable of ferrying a ~50 kg payload with two flights (one for the cable, one for equipment for the cable) . Now, it is reasonable to expect the next decade or so we will produce better fibers, but assume we don't. With one flight, we could build this micro-elevator, send down a small rover or two, and bring up some soil samples. That would I think be worth it, all by itself. If carbon nanofibers earn their promise, we might be able to send up and down a 500 km payload, again with one flight dedicated to carrying cable. That's potentially big enough to carry a person, but, no matter what the payload, we would start gaining information about how to use space elevators. If they prove their worth on the Moon, that will really spur getting the R&D required for a terrestrial one, and I think we would find the resources to make the Lunar cable human capable.
We were launching roughly one Hubble clone per month at the time the Hubble was built, but of course that was for "another program." Doesn't mean that there was the slightest chance we would have built a replacement space telescope in anything less than a decade or two. We wouldn't have, and to pretend otherwise is just that, pretense. Heck, we didn't even have the money to properly test the one we did launch, which is why it went up with a faulty mirror (as did its clones, by the way).
Part of the core problem here is that NASA has been almost entirely taken over by the contractors. They want to build things, or, more exactly, they want to be paid to build things. Having to throw those things away after a relatively short period is to them a feature, not a bug.
I predict the Webb will get to the Lagrange point, work OK for a while, some problem will arise, and the notion of having to go a couple of decades without a functioning space telescope will lead to calls for servicing.
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Well, at least didn't claim the discovery of water on Mars. I think that's been done 4 or 5 times.
I know, I know, as long as it gets it in the papers...
This is IMHO powerful evidence for recent warm wet Mars :
'The other surprising discovery is that ice exposed at the bottom of these meteorite impact craters is so pure,' Byrne said. 'The thinking before was that ice accumulates below the surface between soil grains, so there would be a 50-50 mix of dirt and ice. We were able to figure out, given how long it took that ice to fade from view, that the mixture is about one percent dirt and 99 percent ice.'
'The ice is a relic of a more humid climate not very long ago, perhaps just several thousand years ago.'
Dr. Bryne talks about making this ice through 'frost heave,' but it sounds to me like Arcadia Planitia may have been considerably warmer during the geologically recent past.
Remember, Mars has climate cycles, they cause the sublimation and freezing of both water and Carbon Dioxide, and both water vapor and Carbon Dioxide are powerful greenhouse gases on Mars. (As is methane, which is also present in the Martian atmosphere from unknown sources.) Presumably this ice dates from an earlier part of the climate cycle, when there was higher humidity. Higher humidity implies higher pressure and temperatures. Higher pressures could put the surface above the triple point of water, so that liquid water is possible.
In that case, if the temperature gets high enough, liquid water become inevitable. That would (upon the next change in the climate cycle) freeze as very pure ice.
The Europeans keep talking about sending a rover with a drill to Mars. I think we have now found a good place for it to go.
Indeed. perigee is for Earth orbits.
I agree - most of this is PR, which can be ignored.
To me, the interesting thing is that these layers is that they do not represent a very long history. From Laskar et al. (2002)
For the best fit between the radiance profile and the simulated insolation parameters, we obtain an average deposition rate of 0.05 cm yr-1 for the top 250 m of deposits on the ice cap of the north pole of Mars.
Now, 5 x 10^-4 meters / year means that the top 250 meters represents ~ 500,000 years, and the entire 2 km thick cap represents maybe 5 million years. This is very brief in geological time, and interestingly may be connected to the big change in obliquity thought to have occurred about 5 million years ago. (Note - our ability to predict this back before about 5 million years ago is very poor.)
So, it's likely that not that long ago Mars had no North polar cap, and presumably it comes and goes over geologic time. What happens to the water, and how much the atmosphere increases during these periods, is effectively unknown. While many of the geologists who study Mars think that nothing much has happened there for billions of years, I think that many of the dynamists would disagree.
First, you are aware that the solar output (Solar Constant) has been measured since the 1970's ? There is no need to look at distant worlds to see if it is changing - it varies around at about the 0.1 % level.
Second, I would not put any weight on observations of any body we have not observed for more than one orbit - and that includes Pluto and (for climate) Titan. These are not simple bodies.
The general cause of Pluto's warming is well known - a highly elliptical orbit, and it's near (just past) perigee, where it outgases Methane into the atmosphere. That's one of the motivations behind Pluto Express (to get there while there is still a bigger atmosphere). It is staying warm past perigee, but we have no idea if that is normal or not. Similarly, Titan is passing through the equinox (just as we are here on Earth), and that is causing seasonal change. We know that's happening; we have no idea if what we are seeing is normal or not.
Jupiter is so different from the Earth or Mars that I wouldn't use it as an analogy for anything terrestrial, good or bad. (For example, it generates more heat internally than it gets from the Sun.) Having said that, I had not heard of any warming reported there, so a link would be welcomed.
Well, I have not the slightest doubt that Nathaniel Putzig and company know all about these earlier results - but, once you get the PR people involved, they always want to say, first, confirmed, etc.
No true believers are required.
Unlike the Earth (which has a big Moon to anchor things), Mars has huge variations in insolation due to its obliquity and eccentricity cycles. These oscillations drive large variations in climate, which causes the cool layering in the Martian Polar Caps - the so called North Polar Layered Deposits. There are lots of cool pictures of these layers.
While it is true that both the Earth and Mars would exhibit climate changes if the solar luminosity changed, so far I have not heard of any evidence requiring this from Mars. Mars's internal and orbital dynamics are quite enough to keep the climate modelers busy.
While these results are cool, the obliquity cycle was confirmed in 2002, in a paper in Nature, Orbital forcing of the martian polar layered deposits by Jacques Laskar et al., They used pictures of the layering at the edge of the polar caps, not radar, but its basically the same idea, and they showed good correlation with recent obliquity cycles.
Again, it's cool to see these layers throughout the caps, but I don't think that anyone has doubted the connection with the obliquity / insolation cycles for a while.
That's what I dislike about politicians - they are never willing to wait a few ten-thousand years or so for results !
This sounds a lot like Kudzu - another plant brought over from Japan.
From TFA "For a while, government officials encouraged the use of cogongrass as a forage crop and as a way to stem soil erosion."
We did that with Kudzu too. What's with these agricultural guys promoting alien species they clearly know nothing about ?
Although, if nothing wants to eat it, why promote it as a forage crop ? That does suggest that some animal must like it. There must be some reason why the South of Japan is not one mass of Kudzu and cogongrass.
The point about having nuclear weapons is that people have to care about what you think.
Yes, but expecting the APD to do that fairly is not realistic IMHO. It has to be someone independent.
Let's see, people post on line anonymously, claiming to be police officers, and reporting various abuses.
The police chief "thinks some could be department employees" - translation, he thinks that they are police officers, or, at least, office employees. Implication - either they are telling the truth, or for some other reason hate his guts.
"Acevedo said he and other officers in recent months have faced allegations of sexual impropriety and suggestions that they engaged in quid pro quo behavior."
Translation : he is being accused of having sex with hookers, and letting them go free in return.
As I see it, accusing someone anonymously of these things is whistleblowing. It should be investigated, but by a third party. As it stands, it appears that the police chief is merely trying to find a legal means of finding and punishing whistleblowers. (Any trial would likely amount to the whistleblower saying, "I saw you and X, Y and Z doing this" and the police chief saying "No,you are lying, and here are officers X, Y and Z all willing to testify that you are lying, too." Good luck to the whistleblower on winning that one.)
Now, in a reasonable legal system, this would result in a special prosecutor being appointed. Pardon me for doubting that this will occur in Texas. I would be glad to be proved wrong.
Uh, the title of the actual paper is "Optimal capture trajectories using multiple gravity assists." That is exactly what Galileo Jupiter did - I worked in support of that mission way back in the early 1980's (prior to launch).
Depends on your time horizon. Millions of years, no. Human time horizons, however, we can handle.
A good, modern, numerical integrator at quadruple precision can handle the Sun, planets, and hundreds of asteroids with very small numerical errors (microns over decades). Bigger errors are introduced by observational uncertainty, primarily in the masses of the asteroids. But, even with that, errors are 100's of meters over decades.
This is not new. Almost every mission going further away than Mars or Venus uses these gravity assists, and has since Mariner 10 (1974).
I really dislike the term "gravitational currents." It conveys exactly the wrong impression. The effects of 3rd bodies is almost negligable except during close approaches, so "gravitational billiards" would be much more appropriate.
Sounds sensible to me.
The really interesting thing is that General Relativity predicts two and only two polarizations, while other theories (that cannot be distinguished from G.R. in the usual solar system tests) have more polarizations. If and when we get a good, high SNR, detection of gravitational radiation, a profound test of gravity should follow in short order.
A gravity wave will change the distance to objects at right angles to its direction of propagation. This effect is biggest when the distance to an object is order the wavelength of the wave, or longer. (Since they travel at the speed of light, the relation between wavelength and frequency is the same as for light.) Likewise, the sensitivity is biggest when the period of the wave is between the frequency of measurement and the total duration of observations. So, pulsars are sensitive to waves with periods between about a day (they are not observed continuously) and some decades (the length of data).
Some waves are sinusoidal (distant objects appear to move closer and further away periodically), while impulsive gravitational radiation can have "memory" - i.e., the distance after the burst goes by will be permanently changed.
All of the above assumes we know the correct theory of gravity, which we won't be sure about until we actually get to study them.
LIGO and Pulsars set limits (or could detect) gravitational waves in very different parts of their frequency spectra - periods of milli seconds versus periods of months. The sources are different, the detection physics is different, etc. It's certainly worth trying both.
Also, none of the existing detectors are good enough that you can say for certain that there are known or likely astrophysical sources bright enough that they should see them. You can't talk about falsifiability until you cross that threshold, which I would expect to see happen in a decade or so.
I disagree. Look at the last 30 years of unmanned Mars exploration. We have learned really precious little and at a very slow rate. I am certainly not trying to denigrate the huge amount of effort that has gone into the unmanned effort, but we have basically answered none of the questions raised by the Viking landers. The experiment of relying only on unmanned explorations has been tried, and to me it has very clearly been found wanting.
This is not entirely a matter of technology, but also of politics, but, whatever the causes, I have watched this experiment since Viking, and in my opinion it has very clearly not been a success.
Run rovers on the ground in real time, as opposed to the order one meter per day level. A different type of telepresence.
I agree, but note that a Lunar elevator could be done with existing fibers, like Zylon, No need for new materials for this case (unlike the terrestrial case, where you do).
I actually disagree. You can use existing fiber. Supposed that the heavy lift capability to the Lagrange point is 100 tons. If you dedicated one flight just to lifting your cable, you could build an elevator capable of ferrying a ~50 kg payload with two flights (one for the cable, one for equipment for the cable) . Now, it is reasonable to expect the next decade or so we will produce better fibers, but assume we don't. With one flight, we could build this micro-elevator, send down a small rover or two, and bring up some soil samples. That would I think be worth it, all by itself. If carbon nanofibers earn their promise, we might be able to send up and down a 500 km payload, again with one flight dedicated to carrying cable. That's potentially big enough to carry a person, but, no matter what the payload, we would start gaining information about how to use space elevators. If they prove their worth on the Moon, that will really spur getting the R&D required for a terrestrial one, and I think we would find the resources to make the Lunar cable human capable.
We were launching roughly one Hubble clone per month at the time the Hubble was built, but of course that was for "another program." Doesn't mean that there was the slightest chance we would have built a replacement space telescope in anything less than a decade or two. We wouldn't have, and to pretend otherwise is just that, pretense. Heck, we didn't even have the money to properly test the one we did launch, which is why it went up with a faulty mirror (as did its clones, by the way).
Part of the core problem here is that NASA has been almost entirely taken over by the contractors. They want to build things, or, more exactly, they want to be paid to build things. Having to throw those things away after a relatively short period is to them a feature, not a bug.
I predict the Webb will get to the Lagrange point, work OK for a while, some problem will arise, and the notion of having to go a couple of decades without a functioning space telescope will lead to calls for servicing.