Mars Youth Shows in New Study

The basis for believing Mars is billions of years old and
had oceans like the Earth comes under fire in a new study.

 

 

Science reporters are often a shallow-thinking crowd. They feel their duty is to package scientific consensus with tidy wrapping and deliver it to the peasants. Have you heard that Mars was once like Earth, with oceans and (perhaps) life? Over billions of years, the story goes, Mars was unable to keep its oceans and atmosphere, and it slowly evolved into the frozen desert it is today. Maybe such reporters are philosophically untrained. Maybe they think that critical questions would nudge people toward becoming science deniers. Maybe they just love good stories, true or not. For whatever reason, this is the fluff they often deliver, usually dressed up with visualization effects cheerfully provided by the Art Department.

Science is not tidy. Reading scientific papers often reveals the messy process of consensus formation. But since few have the time or patience to wade through impenetrable jargon in journal papers (if they can even find them), we at CEH do it for you and ask questions that the usual science reporters never think to ask. Mars had oceans? Great. Artist, get busy. Paint us a Mars with beaches and blue lagoons!

Mars may have had abundant water at one time; there is some evidence for that from Mars missions (e.g., 20 Nov 2020). Other evidence could be re-interpreted without water (e.g., 30 July 2021). The question for us today is: how solid is the evidence for Mars oceans? How did scientists arrive at that picture? (6 June 2017). A new paper in Icarus—a major journal of planetary science—casts doubt on one of the primary evidences for Mars oceans. Even more startling, it casts doubt on the billions-of-years story.

Source: Baum, Sholes and Huang, “Impact craters and the observability of ancient martian shorelines,” Icarus, 16 July 2022. Here are the highlights of their models and observations:

• The oldest proposed shorelines (4 Ga) would have been mostly destroyed by direct impacts.
• Shorelines of any age > 3.6 Ga would be dissected into relatively short, discontinuous segments shorter than 40 km.
• Any putative shorelines should exhibit fractal segment lengths with a large number of gaps.

“Putative shorelines” means questionable “claimed” shorelines. We see ancient shorelines on Earth: at Lake Bonneville, in Death Valley, and other places where the evidence is strong. On Mars, however, no humans have ever witnessed large bodies of water. Since the first close orbital images from Mariner 2 in 1962, Mars has been a dry, dusty place scarred by large craters, canyons and volcanoes.

The question becomes: Would shorelines billions of years old survive impact craters? Answer: Probably not. Impacts should have erased them. The older the shorelines (if they existed), the more probable they would have been obliterated.

Notice Point 2 in the Highlights: Any segments of shorelines older than 3.6 billion years (if they existed) would have been dissected into discontinuous segments. The Abstract calls into question prior claims about shorelines 4 billion years old, when Mars was a baby planet.

The existence of possible early oceans in the northern hemisphere of Mars has been researched and debated for decades.

Wait a second; have you heard about debates from science reporters? Or have you just seen the pretty artwork of Mars as an ocean world?

The nature of the early martian climate is still somewhat mysterious, but evidence for one or more early oceans implies long-lasting periods of habitability.

Yes; the astrobiologists like having oceans. It supports their “follow the water” strategy for finding Martian microbes.

The primary evidence supporting early oceans is a set of proposed remnant shorelines circling large fractions of the planet. The primary features are thought to be older than 3.6 Ga and possibly as old as 4 Ga, which would make them some of the oldest large-scale features still identifiable on the surface of Mars.

The alleged shorelines are carrying a lot of evidential weight for the conclusion that Mars once had oceans. The wording of the opening sentences, though, hints at problems ahead:

One question that has not been thoroughly addressed, however, is whether shorelines this old could survive modification and destruction processes like impact craters, tectonics, volcanism, and hydrology in recognizable form. Here we address one of these processes—impact cratering—in detail. We use standard crater counting age models to generate synthetic, global populations of craters and intersect them with hypothetical shorelines, tracking portions of the hypothetical shoreline that are directly impacted.

CEH has noted problems with crater counts as a dating method (e.g., 3 April 2011). The issue here though, is not the dating, but the efficiency of impacts to obliterate those “putative shorelines.” One impact can ruin a Martian’s whole day. (Or should that be sol.) For those truly believing that Mars is older than 4 billion years, this is a problem. They can’t have old ages and shorelines.

The oldest shorelines (4 Ga) are at least 70 % destroyed by direct impacts. Shorelines of any age 3.6 Ga are dissected into relatively short, discontinuous segments no larger than about 40 km when including the effects of craters larger than 100 m in radius. When craters smaller than 500 m in radius are excluded, surviving segment lengths can be as large as 1000 km. The oldest shorelines exhibit fractal structure after impacts, presenting as a discontinuous collection of features over a range of scales. If the features are truly shorelines, high-resolution studies should find similar levels of destruction and discontinuity. However, our results indicate that observing shorelines as old as 4 Ga, should they exist, is a significant challenge and raises questions about prior mapping efforts.

These three researchers found “a significant challenge.” It is so significant that it “raises questions” about their interpretation of shorelines from their maps. Maybe those weren’t shorelines after all. And if they weren’t shorelines, what were those linear features? Maybe they have a different explanation. Maybe they don’t indicate water at all. And without water, what happens to the work of Mars astrobiologists? If they can’t prove vast quantities of water ever existed on Mars, what happens to the major motivation for Mars exploration—the search for life? (see hydrobioscopy, 30 July 2021).

Update 19 July 2022: A new research letter in Geophysical Research Letters on 5 July 2022, “Consolidated Chemical Provinces on Mars: Implications for Geologic Interpretations,” looks at minerals between the northern and southern provinces of Mars and finds limited evidence water had anything to do with the distribution of minerals.

Our findings further reveal that regardless of volatile enrichment, igneous crustal composition dominates over chemical alteration signatures indicating a limited role of liquid water on the martian landscape.

Volcanoes, not water, can explain the “compositional evolution” of the dominant provinces on Mars, the southern highlands and northern lowlands.

The challenge gets worse if you consider a problem with crater count dating not mentioned in the Abstract. Recall the surprise years ago when planetary scientists began to realize the potential for “secondary cratering” (30 Oct 2018). One large impact can launch a million secondary objects that will either fall quickly in ballistic paths or else go into orbit around a body to fall later. Each one of these could make its own crater. This means that a huge number of craters can form in a short period of time. Crater count dating had been based on estimates of rates of incoming meteors from far outside the planet, thinking of “one impactor, one crater.” If one large impact can create hundreds, thousands or millions of secondaries, all bets are off. Some planetary scientists concluded that crater counts are useless for dating a surface (29 Jan 2019).

So here is the tie-in to Mars youth: if these three authors think that so many impacts erased Mars shorelines in 4 Ga, how many secondary craters could erase “putative shorelines” in far less time? The authors are also assuming that Mars had a much thicker atmosphere back then that could support an ocean. Today, water on Mars would quickly sublimate away. The lower gravity of Mars, and its lack of a global magnetic field, would also accelerate the loss of an atmosphere. Given all these challenges, can anyone really maintain the belief that Mars is billions of years old? The rovers observe a very dry surface crackling with static electricity and dust devils. Sometimes there are global dust storms that blanket most of the surface. So what was this about Mars oceans? And given the perchlorates and salts on the surface, what was this hope about life emerging by chance?

We’re just doing our part to look at a “significant challenge” and “raise questions.” You can believe in Mars oceans if you want, if the artwork gives you warm fuzzies. Just don’t base your preference on putative shorelines or putative anything.