My thoughts provoke conditioned minds, while critiquing science & non-science.: Asteroid Vesta

Jan 2012

Vesta Likely Cold and Dark Enough for Ice

https://sservi.nasa.gov/articles/vesta-likely-cold-and-dark-enough-ice/

Though generally thought to be quite dry, roughly half of the giant asteroid Vesta is expected to be so cold and to receive so little sunlight that water ice could have survived there for billions of years, according to the first published models of Vesta's average global temperatures and illumination by the sun.

"Near the north and south poles, the conditions appear to be favorable for water ice to exist beneath the surface," says Timothy Stubbs of NASA's Goddard Space Flight Center in Greenbelt, Md., and the University of Maryland, Baltimore County.

Stubbs and Yongli Wang of the Goddard Planetary Heliophysics Institute at the University of Maryland published the models in the January 2012 issue of the journal Icarus. The models are based on information from telescopes including NASA's Hubble Space Telescope.

Though temperatures on Vesta fluctuate during the year, the model predicts that the average annual temperature near Vesta's north and south poles is less than roughly -200 F (145 K, -128 C). That is the critical average temperature below which water ice is thought to be able to survive in the top 10 feet or so (few meters) of the soil, which is called regolith.

Near Vesta's equator, however, the average yearly temperature is roughly -190F (150 K, -123C), according to the new results. Based on previous modeling, that is expected to be high enough to prevent water from remaining within a few meters of the surface. This band of relatively warm temperatures extends from the equator to about 27 degrees north and south in latitude.

Asteroid Vesta - According to NASA, temperatures below -128C are ideal for water ice to survive in the top few meters of regolith, on the crater floors at Vesta's poles

https://solarsystem.nasa.gov/news/653/vesta-likely-cold-and-dark-enough-for-ice/

But on our moon, no ice was found on the floor of a permanently shadowed crater, despite -163C, as it is too warm for exposed ice to exist on surface. Source - again NASA

So -123C is too warm for ice to exist on the surface or even at few meters below the surface of asteroid Vesta. But comets, despite having even warmer surfaces within the frostline, are expected to have ice on surface & sub-surface !

Many scientists seem weak in temperature physics. The coldest temperature on comet 67P was -93C. Thats too warm for ice to remain on surface & even below the surface. Even the detected ice patches were just a thin coating, most probably created in a endothermic reaction & would sublimate away quickly, without ejecting any dust.

"On average, it's colder at Vesta's poles than near its equator, so in that sense, they are good places to sustain water ice," says Stubbs. "But they also see sunlight for long periods of time during the summer seasons, which isn't so good for sustaining ice. So if water ice exists in those regions, it may be buried beneath a relatively deep layer of dry regolith."

The modeling also indicates that relatively small surface features, such as craters measuring around 6 miles (10 km) in diameter, could significantly affect the survival of water ice. "The bottoms of some craters could be cold enough on average -- about 100 kelvins (-173C) -- for water to be able to survive on the surface for much of the Vestan year [about 3.6 years on Earth]," Stubbs explains. "Although, at some point during the summer, enough sunlight would shine in to make the water leave the surface and either be lost or perhaps redeposit somewhere else."

"The Dawn mission gives researchers a rare opportunity to observe Vesta for an extended period of time, the equivalent of about one season on Vesta," says Stubbs. "Hopefully, we'll know in the next few months whether the GRaND spectrometer sees evidence for water ice in Vesta's regolith. This is an important and exciting time in planetary exploration."

Paper - Illumination conditions at the Asteroid 4 Vesta: Implications for the presence of water ice

- Timothy Stubbs & Yongli Wang, 2012

https://ntrs.nasa.gov/api/citations/20140000992/downloads/20140000992.pdf

Therefore, in the polar regions of Vesta it seems reasonable to expect any significant abundance of water ice to be buried at least a few tens of cm below the surface.

Recent observations of a 3 lm absorption feature on the Moon with band depths of up to 15% indicate that its entire surface is hydrated during some portion of a lunation, with diurnal variations and other characteristics possibly consistent with hydroxyl formed by the interaction between solar wind protons and oxygen-bearing minerals (e.g., Sunshine et al., 2009). The 3 lm absorption feature has also been observed on Vesta (Hasegawa et al., 2003), but the band depth was only 1% which seemed too weak to be consistent with the above solar wind implantation hypothesis. However, the apparent lack of space weathering on Vesta suggests that it is sufficiently magnetized to be able to shield most of its surface from solar wind protons (e.g., Vernazza et al., 2006). This proposed proton-shielding could also be the reason for the relatively weak 3 lm absorption feature, and be indicative of lower than expected abundances of hydrated and/or hydroxylated minerals on the surface of Vesta. Based on our illumination and thermal predictions for present day conditions, it is possible that water ice could have survived in the top few meters of the regolith in the polar regions of Vesta for billions of years (over about half of Vesta’s surface) should it have been delivered there. As expected, topography plays an important role in determining the average illumination conditions and surface temperatures. In particular, small scale topographic features, such as 1–10 km diameter craters, can have a significant effect, and perhaps even permit water ice to be thermally stable at the surface ([100 K) in some polar locations for much of the vestal year.

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2013 paper on Vesta

Curvilinear, interconnecting gullies and associated flow features as evidence for transient water flow on Vesta

https://ui.adsabs.harvard.edu/abs/2013AGUFM.P22A..09S/abstract

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https://en.wikipedia.org/wiki/4_Vesta

Temperatures on the surface have been estimated to lie between about −20 °C (253 K) with the Sun overhead, dropping to about −190 °C (83.1 K) at the winter pole.

No ice despite -190C ?

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March 2012

THE GRAVITY FIELD OF VESTA AND IMPLICATIONS FOR INTERIOR STRUCTURE

https://www.lpi.usra.edu/meetings/lpsc2012/pdf/2600.pdf

May 2012

Dawn at Vesta: Testing the Protoplanetary Paradigm

http://pdfs.semanticscholar.org/7f60/80d89cd0a7a1ee7e49e0bc188c21f220c54b.pdf

Oct 2019

https://www.planetary.org/articles/10091306-what-did-dawn-learn-at-vesta

March 2014

https://www.planetary.org/articles/lpsc-2014-water-on-vesta