'Baby fat' on the young sun?

Feb 14, 2012 By Michael Schirber
Scientists still struggle to understand how the Earth didn't freeze over when the Sun was supposedly fainter. Credit: USC

To deal with the faint young Sun paradox, researchers are taking a fresh look at an old idea: that the Sun started out larger and more luminous than we thought.

Standard models predict that our was much dimmer in its youth, but devising a way to keep the from freezing over has not been easy for climate modelers. An alternative solution – currently being reexamined by a group of stellar modelers -- is to assume our Sun started out a bit heftier (and therefore brighter) than expected.

Most stars tend to increase in luminosity as they get older. This is due to their cores becoming denser and thus hotter over time. Assuming our Sun has followed this same trend, one can estimate that it was 30% fainter 4.5 billion years ago.

"The faint young Sun presents us with a paradox because the predicted temperatures on Earth and Mars would have been too cold for liquid water," explains Steinn Sigurdsson of Penn State University.

Too cold for liquid water? Not likely. Evidence in the oldest rocks suggests that Earth had liquid oceans as far back as 4.4 billion years ago. On Mars, scientists have built up a case that it too was warm and wet around 4 billion years ago.

To avoid the so-called "faint young Sun paradox," scientists over the past 25 years have explored taking the Sun off the "standard" evolution curve. By starting off with a smidgen more mass, the early Sun would be bright enough to maintain liquid water temperatures on Earth and Mars. The catch is that the Sun would need to have had an extremely high solar wind to blow off the excess mass and return it to its "normal weight."

Sigurdsson and his colleagues are tackling this problem anew. With funding from the NASA Astrobiology Institute, they will use improved computer models along with the most recent solar data to compare various scenarios, as well as look for possible signatures in the Sun that might reveal a "crash diet" in its past.

Greenhouse solution

The young massive Sun hypothesis doesn't get a lot of attention these days.

"I think it is a plausible hypothesis, which has not found great favor with the traditional climate science community," says Renu Malhotra of the Lunar Planetary Lab at Arizona State University, who is not involved with this current project. She wonders if others see it as "too easy," like cutting the Gordian knot.

Zircons, like the one shown here, are minerals found in some of the oldest rocks on Earth. They provide evidence of liquid water on Earth over 4 billion years ago. Credit: Stephen Mojzsis

The more popular approach is to try to boost temperatures with an enhanced greenhouse effect.

When Carl Sagan and George Mullen first identified the faint young Sun paradox in 1972, they proposed to solve it by having ammonia, a powerful greenhouse gas, trap heat in the Earth's early atmosphere. But it was later shown that ultraviolet light from the Sun would quickly destroy this ammonia.

Most of the current attention is on models that assume the early Earth was blanketed by large quantities of carbon dioxide (as much as 100 times the current levels). However, this doesn't jive with the geologic record, in which siderite (FeCO3) – a mineral that forms readily in high CO2 conditions – is largely absent in the oldest rock samples.

Even if one could find enough greenhouse gases to keep Earth warm, this route doesn't seem plausible for Mars. Being farther from the Sun, the Red Planet would need an unfeasibly large greenhouse effect. The amount of carbon dioxide needed, for example, is so high that clouds of CO2 begin to form, reflecting heat away rather than trapping it.

"There's no greenhouse solution for Mars," Sigurdsson says. "But geochemists may not be ready to give it up."

Composite image of multiple solar flares on the Sun. How has the Sun evolved over its history? Credit: JAXA

The winds of change

The lack of a clear climate resolution to the paradox leaves the door open for tweaking the initial mass of the Sun.

Previous work has found that this "open door" is really just a "small window," i.e., the increase in solar mass has to be somewhere between 2 and 5 percent. Any less, and the Earth won't warm up enough. Any more, and the Sun evolves into a different star than we know it to be.

Sigurdsson's team is exploring this mass range using a new stellar evolution computer , called MESA, that is more sophisticated than previous ones. The open source code was developed at the Kavli Institute for Physics by Bill Paxton and collaborators.

The mineral siderite (FeCO3) is relatively lacking in ancient rocks, which argues against the early atmosphere being full of carbon dioxide. Credit: Wikipedia

Besides the mass, the researchers can adjust other relevant parameters, like the relative concentration of elements that the Sun starts off with, as well as the degree of turbulence inside the Sun's churning plasma.

"We have a lot more data on the Sun now to tighten the constraints on our models," Sigurdsson says.

The tricky part is to have the solar wind slough off the extra mass in just the right amount of time.

If the current solar wind had been constant over the lifetime of the Sun, then our star would have only lost about 0.05 percent of its mass. Most scientists believe the solar wind was stronger in the past, but how much stronger is debatable.

To provide enough planet warming without overstepping any solar constraints, the Sun had to lose the extra mass in roughly the first few hundred million years, Sigurdsson says. That implies a solar wind that is about 1000 times faster than what we currently observe.

Strong winds have been observed around low mass and high mass stars, but stars like the Sun present less evidence of high wind conditions. Credit: ESO/M. Kornmesser

"You can likely find people that will say it is not feasible, but we need better observations to constrain the models," says Søren Meibom of Harvard University, who is also not involved with the project.

Strong winds are known to exist around high mass and low mass stars, but medium-sized stars like our Sun don't appear to be as windy.

"It is quite challenging to find strong support for [a massive young Sun] in astronomical observations of young Sun-like stars," Malhotra says. "Young Sun-like stars appear to lose mass initially very quickly."

Stellar stretch marks

If the Sun did lose a significant amount of mass in its youth, we might expect some telltale sign in solar system data. Some meteorites, for example, show crystal damage that appears to come from a stronger , but just how much stronger is not yet known.

In 2007, Malhotra and David Minton, who's currently at Purdue University, looked to see if the orbital dynamics of the solar system could hold any signatures of a massive young Sun. For instance, the planets would have started out in tighter orbits due to the Sun's stronger gravity. But it turns out the difference is too small to have left any noticeable traces.

According to Malhotra and Minton, the most promising place to look for an orbit-related signature would be in the distribution of irregular satellites, which are moons like Saturn's Phoebe and Jupiter's Himalia that are in distant, inclined orbits. As the Sun loses mass, it could increase the efficiency at which planets can capture irregular moons. Malhotra says she plans to study this effect more closely in the future.

The goal of Sigurdsson's project is to look in the Sun itself for some leftover changes, or "stretch marks," from an earlier, more massive period. They hope to find something that would be detectable with future helioseismology observations.

"The core of the Sun will hopefully provide us with some sort of sign," he says.

Explore further: The changing laws that determine how dust affects the light that reaches us from the stars

Related Stories

Stellar winds

Oct 10, 2011

(PhysOrg.com) -- The Sun, glowing with a surface temperature of about 5500 degrees Celsius, warms the Earth with its salutary light. Meanwhile the Sun's hot outer layer (the corona), with its temperature of ...

The Sun Loses its Spots

Jul 24, 2007

While sidewalks crackle in the summer heat, NASA scientists are keeping a close eye on the sun. It is almost spotless, a sign that the Sun may have reached solar minimum. Scientists are now watching for the ...

Making massive stars

Aug 29, 2011

How do massive stars form? Stars with more than about eight times as much mass as the sun are arguably the most important actors in the universe. Although they live only hundreds of millions of years, they ...

Stars: How big is big?

Dec 12, 2011

You may have seen one of these astronomical scale picture sequences, where you go from the Earth to Jupiter to the Sun, then the Sun to Sirius – and all the way up to the biggest star we know of VY Canis ...

A 360 degree view of an X-class flare and a CME

Nov 08, 2011

(PhysOrg.com) -- The sun sent out two different kinds of solar activity last night in different directions. One was an X 1.9 class flare that burst out from an active region on the sun, numbered AR1339, which ...

ESA To Collaborate with NASA on Solar Science Mission

Oct 06, 2011

On October 4, 2011, the European Space Agency announced it's two next science missions, including Solar Orbiter, a spacecraft geared to study the powerful influence of the sun. Solar Orbiter will be an ESA-led ...

Recommended for you

ESO image: A study in scarlet

9 hours ago

This new image from ESO's La Silla Observatory in Chile reveals a cloud of hydrogen called Gum 41. In the middle of this little-known nebula, brilliant hot young stars are giving off energetic radiation that ...

Astronomers: 'Tilt-a-worlds' could harbor life

Apr 15, 2014

A fluctuating tilt in a planet's orbit does not preclude the possibility of life, according to new research by astronomers at the University of Washington, Utah's Weber State University and NASA. In fact, ...

Pushy neighbors force stellar twins to diverge

Apr 15, 2014

(Phys.org) —Much like an environment influences people, so too do cosmic communities affect even giant dazzling stars: Peering deep into the Milky Way galaxy's center from a high-flying observatory, Cornell ...

Image: Multiple protostars within IRAS 20324+4057

Apr 14, 2014

(Phys.org) —A bright blue tadpole appears to swim through the inky blackness of space. Known as IRAS 20324+4057 but dubbed "the Tadpole", this clump of gas and dust has given birth to a bright protostar, ...

User comments : 13

Adjust slider to filter visible comments by rank

Display comments: newest first

4.6 / 5 (5) Feb 14, 2012
Maybe I'm missing something but as Earth was being formed was it not very hot with geothermal energy from the ton of debris impacts giving us our molten core. Does it stand to reason that the planet itself was hot enough to sustain the liquid water and gradually cooled alongside the sun heating up?
1 / 5 (11) Feb 14, 2012
The solar wind is increasing the opacity of space within the solar system. This opacity to visible light gives the appearance of an expanding universe. The opacity to infrared reduces the heat from the sun even as the sun is heating up. Voyager did not detect solar wind at the edge of the solar system, so all of the solar particles are still around.
1 / 5 (1) Feb 14, 2012
I would tend to agree with Geothermal as the source of heat that kept the water as a liquid. Plate tectonics can only be dated back to 3.8 billion years so logically the earth was alot flatter on the surface up until that time. However being very young, it stands to reason that it was hotter in each layer through to the core and volcanism was far more prevalent, along with frequent impacts. I don't think the sun's evolution has to change to explain this, although it still doesn't explain mars. One other option is that the sun is slightly older than thought and had time to heat up before the planets completely formed.
3.9 / 5 (7) Feb 14, 2012
Maybe inner SS planets move around a bit because the outter solar system isn't entirely stable.

I.E. when Pluto crosses Neptune's orbit, this should transfer some moementum between the two. Then, because Neptune's orbit is changed, there should be a gradual "tricke down" effect throughout the major planets in the solar system. In order to conserve angular momentum, some planets must move inward, and others must move outwards.

This explains changes in temperature without invoking drastic changes in the Sun.
Uh oh. QC is attempting celestial mechanics again. In his head. Remember the last time you did this and people made you look like a fool? Wanna bet its going to happen again?
so when you try to explain Earth's water by invoking COMETS it is unnecessary.
-which is why scientists who actually know what theyre talking about, propose it -? Maybe they would consider your insane blathering ...unnecessary?
5 / 5 (7) Feb 14, 2012
In this thread: people demonstrating the Dunning-Kruger effect

1 / 5 (2) Feb 14, 2012
mmm... y couldn;t the Earth have been frozen -- wouldn;t that actually make things a little easier to ??
3 / 5 (4) Feb 14, 2012
We know that the sea floor is composed of denser rock than continental crust, and so it sank over time, while continental crust is less dense and rose over time.
Uh you have a source for this besides your poor wounded brain? Can you feel the remnants of it sloshing about when you sneeze?

His explanation is crude at best. There was very little continental crust about 4B years ago. Continental crust is formed when oceanic crust differentiates as it is being subducted, hence the lighter parts rising to form continental crust and the denser parts of the oceanic rock sink. Estimates place only 10% of existing continental crust at 3.7B, 25% at 3B, and 60% at 2.6B years ago.

2.3 / 5 (3) Feb 14, 2012
Danke. Usually I will go look these things up and I would have read this:

"All continental crust ultimately derives from the fractional differentiation of oceanic crust over many eons. This process has been and continues today primarily as a result of the volcanism associated with subduction."

-which I did not know.
1 / 5 (1) Feb 15, 2012
Danke. Usually I will go look these things up and I would have read this:

"All continental crust ultimately derives from the fractional differentiation of oceanic crust over many eons. This process has been and continues today primarily as a result of the volcanism associated with subduction."

-which I did not know.

@ Lurker, the above quote sums up the reasoning for the sea floor vs. continental crust argument. The liquid oceans were here 4.4 billion years ago, plate tectonics have only been around for app. 3.8 billion. At the time of the liquid water there would have been no differentiating the earths crust between oceanic and continental. There wouldn't have been subduction zones to create the continental crust yet. No question of the geology, but the timing doesn't fit.
5 / 5 (3) Feb 15, 2012
There is less of "a faint young Sun paradox" than ever.

Since Kasting did his estimates, AGW has both forced and enabled better GW modeling. The necessary CO2 has decreased with 1-2 order of magnitudes.

From the other end, geologists have discovered early ocean siderites and are arguing whether there the land absence is because of early soil bacteria prohibiting its formation ("Low pCO2 in the pore water, not in the Archean air", Daphas & Kasting (!), Nature 2010.)

On the thread: Superstition driven creationist trolling on science is absurd.
5 / 5 (2) Feb 16, 2012
Thank you mods for finally doing your jobs and removing all the OT religious spew. I only engage that stuff because reporting it is usually pointless. So thanks.

Back on topic: I think the evidence that the earth was not frozen over seems a bit light. At least from what is presented here. Plus the fact that you need to finely tune the young sun and tweak models in all manner of ways. It all seems to point the fact that the sun was cold and dim 4B years ago.

not rated yet Feb 27, 2012
Hot gas? or a binary twin?
1 / 5 (1) Feb 27, 2012
Young Earth had a much higher concentration of unstable isotopes, so it could heat itself geothermaly.

In this thread: people demonstrating the Dunning-Kruger effect
OK, but why to demonstrate it with posting of this sentence into every thread?

More news stories

Meteorites yield clues to Martian early atmosphere

(Phys.org) —Geologists who analyzed 40 meteorites that fell to Earth from Mars unlocked secrets of the Martian atmosphere hidden in the chemical signatures of these ancient rocks. Their study, published ...

Let's put a sailboat on Titan

The large moons orbiting the gas giants in our solar system have been getting increasing attention in recent years. Titan, Saturn's largest moon, is the only natural satellite known to house a thick atmosphere. ...

US judge overturns state's abortion law

A federal judge on Wednesday overturned a North Dakota law banning abortions when a fetal heartbeat can be detected, as early as six weeks into pregnancy and before many women know they're pregnant.