Explanation: On a mission to explore the inner heliosphere and solar corona, on July 11, 2020 the Wide-field Imager on board NASA's Parker Solar Probe captured this stunning view of the nightside of Venus at distance of about 12,400 kilometers (7,693 miles). The spacecraft was making the third of seven gravity-assist flybys of the inner planet. The gravity-asssist flybys are designed to use the approach to Venus to help the probe alter its orbit to ultimately come within 6 million kilometers (4 million miles) of the solar surface in late 2025. A surprising image, the side-looking camera seems to peer through the clouds to show a dark feature near the center known as Aphrodite Terra, the largest highland region on the Venusian surface. The bright rim at the edge of the planet is nightglow likely emitted by excited oxygen atoms recombining into molecules in the upper reaches of the atmosphere. Bright streaks and blemishes throughout the image are likely due to energetic charged particles, and dust near the camera reflecting sunlight. Skygazers from planet Earth probably recognize the familiar stars of Orion's belt and sword at lower right.
Nice Orion in the background! I particularly appreciate Lambda Orionis and friends just below center in the APOD.
Ann
I wonder whether Venus would have been a habitable planet if, a few billion years ago, it had experienced a collision with a planetoid, such as the one that created the Earth's Moon, and also removed much, but not all of the the then Earth's atmosphere. Had that collision not occurred, would the Earth now have a thick atmosphere and have experienced the 'runaway greenhouse' effect that gives Venus its surface temperature above the melting point of lead?
Re: APOD: A Venus Flyby (2021 Feb 25)
Posted: Thu Feb 25, 2021 3:04 pm
by sp0ck
I'm sure someone else saw this and has a reasonable explanation:
Chip in the camera lens?
Spacebug splattered on the "windshield"?
Or just a (boring!) processing glitch?
Re: APOD: A Venus Flyby (2021 Feb 25)
Posted: Thu Feb 25, 2021 3:43 pm
by shaileshs
sp0ck wrote: ↑Thu Feb 25, 2021 3:04 pm
I'm sure someone else saw this and has a reasonable explanation:
Chip in the camera lens?
Spacebug splattered on the "windshield"?
Or just a (boring!) processing glitch?
Yep, I was wondering exactly same.
Re: APOD: A Venus Flyby (2021 Feb 25)
Posted: Thu Feb 25, 2021 3:47 pm
by Chris Peterson
sp0ck wrote: ↑Thu Feb 25, 2021 3:04 pm
I'm sure someone else saw this and has a reasonable explanation:
Chip in the camera lens?
Spacebug splattered on the "windshield"?
Or just a (boring!) processing glitch?
From the original (linked) press release: The dark spot appearing on the lower portion of Venus is an artifact from the WISPR instrument.
Re: APOD: A Venus Flyby (2021 Feb 25)
Posted: Thu Feb 25, 2021 3:56 pm
by Ann
Eclectic Man wrote: ↑Thu Feb 25, 2021 2:51 pm
I wonder whether Venus would have been a habitable planet if, a few billion years ago, it had experienced a collision with a planetoid, such as the one that created the Earth's Moon, and also removed much, but not all of the the then Earth's atmosphere. Had that collision not occurred, would the Earth now have a thick atmosphere and have experienced the 'runaway greenhouse' effect that gives Venus its surface temperature above the melting point of lead?
I think Venus would probably have been too hot anyway, because it is too close to the Sun. The way I remember it, when the "un-habitability" of Venus was first discovered (or at least openly acknowledged, or at least acknowledged in my local paper in Sweden), Venus was "supposed" to be around 80-90°C. That would have made it rather uncomfortably hot in any case (or at least I think so) but perhaps habitable. At a temperature of 80-90°C, Venus would have been very sensitive to climate change, and any living organisms that were dependent on below-100°C temperatures could so easily have perished.
But one way or another, the incredibly thick atmosphere of Venus helped casue a runaway greenhouse effect, raising the temperature of Venus to some 400°C.
While I don't know the exact cause of this runaway greenhouse effect, I doubt that a collision with a Mars-sized body could have saved Venus from crazily heating up itself.
Eclectic Man wrote: ↑Thu Feb 25, 2021 2:51 pm
I wonder whether Venus would have been a habitable planet if, a few billion years ago, it had experienced a collision with a planetoid, such as the one that created the Earth's Moon, and also removed much, but not all of the the then Earth's atmosphere. Had that collision not occurred, would the Earth now have a thick atmosphere and have experienced the 'runaway greenhouse' effect that gives Venus its surface temperature above the melting point of lead?
I think Venus would probably have been too hot anyway, because it is too close to the Sun. The way I remember it, when the "un-habitability" of Venus was first discovered (or at least openly acknowledged, or at least acknowledged in my local paper in Sweden), Venus was "supposed" to be around 80-90°C. That would have made it rather uncomfortably hot in any case (or at least I think so) but perhaps habitable. At a temperature of 80-90°C, Venus would have been very sensitive to climate change, and any living organisms that were dependent on below-100°C temperatures could so easily have perished.
But one way or another, the incredibly thick atmosphere of Venus helped casue a runaway greenhouse effect, raising the temperature of Venus to some 400°C.
While I don't know the exact cause of this runaway greenhouse effect, I doubt that a collision with a Mars-sized body could have saved Venus from crazily heating up itself.
Ann
So I presume that the habitable zone is narrower than at first thought !
Eclectic Man wrote: ↑Thu Feb 25, 2021 2:51 pm
I wonder whether Venus would have been a habitable planet if, a few billion years ago, it had experienced a collision with a planetoid, such as the one that created the Earth's Moon, and also removed much, but not all of the the then Earth's atmosphere. Had that collision not occurred, would the Earth now have a thick atmosphere and have experienced the 'runaway greenhouse' effect that gives Venus its surface temperature above the melting point of lead?
I think Venus would probably have been too hot anyway, because it is too close to the Sun. The way I remember it, when the "un-habitability" of Venus was first discovered (or at least openly acknowledged, or at least acknowledged in my local paper in Sweden), Venus was "supposed" to be around 80-90°C. That would have made it rather uncomfortably hot in any case (or at least I think so) but perhaps habitable. At a temperature of 80-90°C, Venus would have been very sensitive to climate change, and any living organisms that were dependent on below-100°C temperatures could so easily have perished.
But one way or another, the incredibly thick atmosphere of Venus helped casue a runaway greenhouse effect, raising the temperature of Venus to some 400°C.
While I don't know the exact cause of this runaway greenhouse effect, I doubt that a collision with a Mars-sized body could have saved Venus from crazily heating up itself.
Ann
So I presume that the habitable zone is narrower than at first thought :shock: !
Actually, I think it's gotten wider, with both Venus and Mars now solidly inside of it. That's because we understand a lot more about extremophiles, and a lot more about how life can exist in zones that are protected such that liquid water can exist. Of course, "habitable" is a poor choice of words, but one that has largely stuck. The zone that is "habitable" in terms of complex life is much narrower than the zone that simply might support life in its simpler forms.
Ann wrote: ↑Thu Feb 25, 2021 3:56 pm
I think Venus would probably have been too hot anyway, because it is too close to the Sun. The way I remember it, when the "un-habitability" of Venus was first discovered, Venus was "supposed" to be around 80-90°C. That would have made it rather uncomfortably hot in any case (or at least I think so) but perhaps habitable. At a temperature of 80-90°C, Venus would have been very sensitive to climate change, and any living organisms that were dependent on below-100°C temperatures could so easily have perished.
So I presume that the habitable zone is narrower than at first thought !
Actually, I think it's gotten wider, with both Venus and Mars now solidly inside of it. That's because we understand a lot more about extremophiles, and a lot more about how life can exist in zones that are protected such that liquid water can exist. Of course, "habitable" is a poor choice of words, but one that has largely stuck. The zone that is "habitable" in terms of complex life is much narrower than the zone that simply might support life in its simpler forms.
<<Alvinella pompejana, the Pompeii worm, is a species of deep-sea polychaete worm (commonly referred to as "bristle worms"). It is an extremophile found only at hydrothermal vents in the Pacific Ocean, discovered in the early 1980s off the Galápagos Islands by French marine biologists.
They can reach up to 13 cm in length and are pale gray, with red tentacle-like gills on their heads. Perhaps most fascinating, their tail ends are often resting in temperatures as high as 80 °C, while their feather-like heads stick out of the tubes into water that is a much cooler, 22 °C. Scientists are attempting to understand how Pompeii worms can withstand such extreme temperatures by studying the bacteria that form a "fleece-like" covering on their backs. Living in a symbiotic relationship, the worms secrete mucus from tiny glands on their backs to feed the bacteria, and in return, they are protected by some degree of insulation. The bacteria have also been discovered to be chemolithotrophic, contributing to the ecology of the vent community. Recent research suggests the bacteria might play an important role in the feeding of the worms.
Attaching themselves to black smokers, the worms have been found to thrive at sustained temperatures of from 45 to 60 °C and even 105 °C for a short time, making the Pompeii worm the most heat-tolerant complex animal known to science after the tardigrades (or water bears), which are able to survive temperatures over 150 °C. >>
<<The Venus flytrap (Dionaea muscipula) is a carnivorous plant native to subtropical wetlands on the East Coast of the United States in North Carolina and South Carolina. The Venus flytrap is found in nitrogen- and phosphorus-poor environments, such as bogs and wet savannahs. Small in stature and slow-growing, the Venus flytrap tolerates fire well and depends on periodic burning to suppress its competition. Fire suppression threatens its future in the wild. It survives in wet sandy and peaty soils. Although it has been successfully transplanted and grown in many locales around the world, it is native only to the coastal bogs such as North Carolina's Green Swamp. There also appears to be a naturalized population of Venus flytraps in northern Florida as well as an introduced population in western Washington. The nutritional poverty of the soil is the reason it relies on such elaborate traps: insect prey provide the nitrogen for protein formation that the soil cannot.
They are full sun plants, usually found only in areas with less than 10% canopy cover. The microhabitat where it thrives is typically sparse with grasses, herbs, sphagnum, and often bare patches where there aren't enough nutrients for noncarnivorous plants to survive, or where fires regularly clear competition and prevent cover from forming. Thus, natural fires are an important part of its habitat, required every 3–5 years in most places for D. muscipula to thrive. After fire, D. muscipula seeds germinate well in ash and sandy soil, with seedlings growing well in the open post-fire conditions. The seeds germinate immediately without a dormant period.>>
Re: APOD: A Venus Flyby (2021 Feb 25)
Posted: Thu Feb 25, 2021 11:41 pm
by VictorBorun
Chris Peterson wrote: ↑Thu Feb 25, 2021 4:38 pm
The zone that is "habitable" in terms of complex life is much narrower than the zone that simply might support life in its simpler forms.
I protest.
Why proclaim xeno extremophiles primitive?
Here on Earth we see just one example of an evolution, global for Earth and isolated from xeno-life.
Once a complex species emerges it successfully occupies the niche and block it from intruders.
But what if it never emerged? The niche would be free for other tries.
Can an extremophile left to its own devices evolve into a comlex extremophile, we have no idea.
Chris Peterson wrote: ↑Thu Feb 25, 2021 4:38 pm
The zone that is "habitable" in terms of complex life is much narrower than the zone that simply might support life in its simpler forms.
I protest.
Why proclaim xeno extremophiles primitive?
Here on Earth we see just one example of an evolution, global for Earth and isolated from xeno-life.
Once a complex species emerges it successfully occupies the niche and block it from intruders.
But what if it never emerged? The niche would be free for other tries.
Can an extremophile left to its own devices evolve into a comlex extremophile, we have no idea.
Simple life means single celled organisms, or simple colonies of them.
Complex life means multi-cellular organisms.
It isn't a question of primitive. It's simply that the more complex the life is, the more fragile it is. The more sensitive it will be to environmental perturbations. The fewer niches that it can survive in.
Re: APOD: A Venus Flyby (2021 Feb 25)
Posted: Sat Feb 27, 2021 3:36 am
by Dmpalmer
If that’s the night side, what is the source of light? Is this the ‘ashen glow’ that some observers have seen on the night side of Venus from Earth?
Possibilities: airglow or other chemical reactions in the atmosphere; sunlight scattered through the atmosphere from the dayside; infrared light from the hot surface making it past the optics filters; bioluminescence from aerial plankton. (That last one is well above the ‘Oumuamua lightsail probability in my opinion, so almost certainly wrong.)
The streaks don’t look like cosmic rays. They aren’t affiliated with Venus (not moving fast enough in the spacecraft frame, ludicrously high in number to be something that fills all of circum-Venus space at that density). They must be dust or other particulates from the spacecraft.
It would be interesting to see another exposure like this once Parker is far from planets. I bet that the same type of streaks will be there. But maybe they are shaken off of Parker by thruster fires or other actions taken during flybys.
Re: APOD: A Venus Flyby (2021 Feb 25)
Posted: Sat Feb 27, 2021 4:50 pm
by Dmpalmer
Dmpalmer wrote: ↑Sat Feb 27, 2021 3:36 am
If that’s the night side, what is the source of light?
...
infrared light from the hot surface making it past the optics filters; bioluminescence from aerial plankton.
...
Answering myself: probably infrared light, in WISPR's nominal band.
WISPR specs: 0.42 cm^2 aperture, 490-740 nm bandpass (for camera which goes deeper into red)
gives 3.7e9 photons per second per steradian, which means something like a billion photons per second would hit the full frame detector and each pixel would get about a thousand photons per second if pointed at Venus.
The Venus part of the image looks about right for a thousand photons per second with reasonable exposure.
So we are seeing the thermal glow of the hot surface of Venus, and it appears that the highlands such as Aphrodite Terra are either cooler or less emissive than the lowlands, hence darker.
Dmpalmer wrote: ↑Sat Feb 27, 2021 3:36 am
If that’s the night side, what is the source of light?
...
infrared light from the hot surface making it past the optics filters; bioluminescence from aerial plankton.
...
Answering myself: probably infrared light, in WISPR's nominal band.
WISPR specs: 0.42 cm^2 aperture, 490-740 nm bandpass (for camera which goes deeper into red)
gives 3.7e9 photons per second per steradian, which means something like a billion photons per second would hit the full frame detector and each pixel would get about a thousand photons per second if pointed at Venus.
The Venus part of the image looks about right for a thousand photons per second with reasonable exposure.
So we are seeing the thermal glow of the hot surface of Venus, and it appears that the highlands such as Aphrodite Terra are either cooler or less emissive than the lowlands, hence darker.
FWIW, the linked press release explains that we're seeing thermal glow, and that the streaks are mostly dust and debris following the spacecraft.
Re: APOD: A Venus Flyby (2021 Feb 25)
Posted: Mon Mar 01, 2021 4:33 am
by Dmpalmer
I grabbed some images from the website and found some long exposures* with the spacecraft in motion, rotating to streak the stars.
The rotation also causes the dust streaks to curve (linear motion of dust combined with rotational motion of spacecraft and camera) and demonstrates that those streaks are not due to cosmic rays hitting the detector or even orbital-speed space dust.
The press release didn't say which features were cosmic ray hits (the dozen or so short or point-like spots that aren't stars) which are dust/debris from the spacecraft itself (the long streaks, straight in the original picture, curved in this one) and which are space dust (I am guessing there are zero visible features due to natural space dust in this picture.)
*(Selecting >10s exposure and 2020-07-11 3:00 - 3:45. The attached image is 03:32:45)
Re: APOD: A Venus Flyby (2021 Feb 25)
Posted: Mon Mar 01, 2021 2:49 pm
by neufer
Re: APOD: A Venus Flyby (2021 Feb 25)
Posted: Tue Mar 02, 2021 12:11 am
by VictorBorun
Chris Peterson wrote: ↑Fri Feb 26, 2021 1:09 am
the more complex the life is, the more fragile it is
True for what we see on Earth. We have large volumes of liquid almost pure water at 0…100°C, and those are ruled by complex life forms, and only the extreme periphery is left without their domination.
But what if a hot or a cold extreme is all there is? One cell extremophile life forms could evolve into something more complex, for all we know.
Maybe multi-cell, maybe using two sexes for reproduction, maybe using chemical and electric messaging within an individual organism or between organisms, — but based on extremophile subcell mechanisms.
Chris Peterson wrote: ↑Fri Feb 26, 2021 1:09 am
the more complex the life is, the more fragile it is
True for what we see on Earth. We have large volumes of liquid almost pure water at 0…100°C, and those are ruled by complex life forms, and only the extreme periphery is left without their domination.
But what if a hot or a cold extreme is all there is? One cell extremophile life forms could evolve into something more complex, for all we know.
Maybe multi-cell, maybe using two sexes for reproduction, maybe using chemical and electric messaging within an individual organism or between organisms, — but based on extremophile subcell mechanisms.
I can't think of any case where multicellular organisms wouldn't be more complex, or where more complex life forms wouldn't be more fragile and sensitive to environmental changes. Even on Earth, complex life is recent, and has undergone numerous massive extinctions, and would do so again under all sorts of conditions, like Earth's orbit being changed a bit, a large asteroid impact, a nearby supernova.
the more complex the life is, the more fragile it is
True for what we see on Earth. We have large volumes of liquid almost pure water at 0…100°C, and those are ruled by complex life forms, and only the extreme periphery is left without their domination.
But what if a hot or a cold extreme is all there is? One cell extremophile life forms could evolve into something more complex, for all we know. Maybe multi-cell, maybe using two sexes for reproduction, maybe using chemical and electric messaging within an individual organism or between organisms, — but based on extremophile subcell mechanisms.
Eclectic Man wrote: ↑Thu Feb 25, 2021 2:51 pm
I wonder whether Venus would have been a habitable planet if, a few billion years ago, it had experienced a collision with a planetoid, such as the one that created the Earth's Moon, and also removed much, but not all of the the then Earth's atmosphere. Had that collision not occurred, would the Earth now have a thick atmosphere and have experienced the 'runaway greenhouse' effect that gives Venus its surface temperature above the melting point of lead?
What if there was low density atmosphere on Venus, and then there was some cosmic spores infection, and then Venus got hotter and life retreated to polar caps and mountain peaks and dust in the upper atmosphere, and then it found a way to make cellar cytoplasma so thick that it would not boil up to 300°C and re-designed all the protein machines rely on 300°C to be moving as vivid as needed?
Re: APOD: A Venus Flyby (2021 Feb 25)
Posted: Sun Mar 07, 2021 12:20 am
by Psalm19-1
Curious: How did this probe manage to photograph the surface of Venus? And at night no less??
Re: APOD: A Venus Flyby (2021 Feb 25)
Posted: Sun Mar 07, 2021 12:44 am
by Chris Peterson
Psalm19-1 wrote: ↑Sun Mar 07, 2021 12:20 am
Curious: How did this probe manage to photograph the surface of Venus? And at night no less??
Because we're seeing a wavelength that represents thermal IR, where the atmosphere is slightly transparent, and where the source is the surface itself, not reflected sunlight.
First Images of Venus' Surface in Visible Light, Confirmed
NASA’s Parker Solar Probe has taken its first visible light images of the surface of Venus from space.
Smothered in thick clouds, Venus’ surface is usually shrouded from sight. But in two recent flybys of the planet, Parker used its Wide-Field Imager, or WISPR, to image the entire nightside in wavelengths of the visible spectrum – the type of light that the human eye can see – and extending into the near-infrared.
The images, combined into a video, reveal a faint glow from the surface that shows distinctive features like continental regions, plains, and plateaus. A luminescent halo of oxygen in the atmosphere can also be seen surrounding the planet. ...
The first WISPR images of Venus were taken in July 2020 as Parker embarked on its third flyby, which the spacecraft uses to bend its orbit closer to the Sun. WISPR was designed to see faint features in the solar atmosphere and wind, and some scientists thought they might be able to use WISPR to image the cloud tops veiling Venus as Parker passed the planet. ...
But instead of just seeing clouds, WISPR also saw through to the surface of the planet. The images were so striking that the scientists turned on the cameras again during the fourth pass in February 2021. During the 2021 flyby, the spacecraft’s orbit lined up perfectly for WISPR to image Venus’ nightside in entirety. ...
A Venus Flyby
I particularly appreciate Lambda Orionis and friends just below center in the APOD.
!
