Hunting for hidden life on worlds orbiting old, red stars

Hunting for hidden life on worlds orbiting old, red stars
This graphic shows where a planet can be habitable and warm around our sun, as it ages over billions of years. Credit: Cornell University

All throughout the universe, there are stars in varying phases and ages. The oldest detected Kepler planets (exoplanets found using NASA's Kepler telescope) are about 11 billion years old, and the planetary diversity suggests that around other stars, such initially frozen worlds could be the size of Earth and could even provide habitable conditions once the star becomes older. Astronomers usually looked at middle-aged stars like our sun, but to find habitable worlds, one needs to look around stars of all ages.

In their work, Ramses M. Ramirez, research associate at Cornell's Carl Sagan Institute and Lisa Kaltenegger, associate professor of astronomy and director of the Carl Sagan Institute, have modeled the locations of the for aging and how long can stay in it. Their research, "Habitable Zones of Post-Main Sequence Stars," is published in the Astrophysical Journal May 16.

The "habitable zone" is the region around a star in which water on a planet's surface is liquid and signs of life can be remotely detected by telescopes.

"When a star ages and brightens, the habitable zone moves outward and you're basically giving a second wind to a planetary system," said Ramirez. "Currently objects in these outer regions are frozen in our own solar system, and Europa and Enceladus - moons orbiting Jupiter and Saturn - are icy for now."

Dependent upon the mass (weight) of the original star, planets and their moons loiter in this red giant habitable zone up to 9 billion years. Earth, for example, has been in our sun's habitable zone so far for about 4.5 billion years, and it has teemed with changing iterations of life. However, in a few billion years our sun will become a red giant, engulfing Mercury and Venus, turning Earth and Mars into sizzling rocky planets, and warming distant worlds like Jupiter, Saturn and Neptune - and their moons - in a newly established red giant habitable zone.

"Long after our own plain yellow sun expands to become a red giant star and turns Earth into a sizzling hot wasteland, there are still regions in our solar system - and other solar systems as well - where life might thrive," says Kaltenegger.

"For stars that are like our sun, but older, such thawed planets could stay warm up to half a billion years in the red giant habitable zone. That's no small amount of time," said Ramirez, who is the lead author of the study.

"In the far future, such worlds could become habitable around small red suns for billions of years, maybe even starting life, just like Earth. That makes me very optimistic for the chances for life in the long run," said Kaltenegger.

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More information: "Habitable Zones of Post-Main Sequence Stars," Ramses M. Ramirez & Lisa Kaltenegger, 2016 May 16, Astrophysical Journal Preprint: … 342293/65288426425/1
Journal information: Astrophysical Journal

Provided by Cornell University
Citation: Hunting for hidden life on worlds orbiting old, red stars (2016, May 16) retrieved 16 September 2019 from
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May 16, 2016
It appears the red giant phase of a star is relatively small percentage of that star's overall lifetime. Yes, the outer parts of our solar system will get some habitable zone love for a while when Earth is incinerated (unless somehow protected), but some sources indicate our sun's red giant phase will last less than 1 billion years. That is plenty of time for our descendants to move out there, but probably not enough for complex multi-cellular life to evolve like it did on Earth. So the "second wind" for the solar system is relatively short.

May 16, 2016
@Sonhouse: The average species lifetime is ~2 million years among mammals, so we should still be much the same species in a million years. (We are just 0.2 million years old.)

May 16, 2016
Sonhouse and Torbjorn raise good points, but extinction is not the only option. By some measure, Homo Erectus evolved into Homo Sapiens, and there will be a next step for us too.

For the average person, the take-away lesson here is we are destined to do big things in space because the alternative does not look to be very pleasant. Other alien cultures would get the same lesson once their understanding of science is advanced enough. So the question becomes are we the type of intelligent race that can read the writing on the wall and act accordingly, or are we just another species doomed to extinction?

May 17, 2016
The article is from the time of ancient Greece.
In our galaxy there are 200 to 400 billion stars (star system) and can not be, to make a conclusion based on one star (one star system).
Evidence from observations of the Universe are going in the opposite direction, more dwarfs are not defunct old star already small stars (there are over 77% of the total number of stars in the Milky Way), "inflated" star has a less than 1 in a million stars. The red color of the stars does not bind more, along "inflatable" stars (76.45 red stars are dwarfs) ...

http://www.svemir...tml#Life "The Wrong Ideas About Life Creating Zones"

May 17, 2016
@Mark: I didn't make it explicit, but the mammalian average is between speciations.

While 99.9 % of species has gone extinct, there is no reason to predict that any specific [sic!] species will go extinct.

I thought Sonhouse was jesting against better knowledge, or possibly making incredulous claims. Considering our large populations , our species is now more resilient than most. (Large allele pool; efficient selection mechanism in large populations; and pf course the very population size helps.)

@wduckss: Of course one sample of a process suffice to say a lot, it isn't like we are sampling an event. Statistics 101. (Or Stochastic processes 101, perhaps.)

The last part of your comment is illegible.

May 17, 2016
"Hunting for hidden life on worlds orbiting old, red stars."

This can be named with one word: Desperation

Physical and moral laws are not written by themselves. For this is needed intelligence of intelligent being. They always reflect the ideas of intelligent beings to maintain their order according to their moral principles.

May 17, 2016
viko_mx 1 /5 (3)

This can be named with two words: Oxygen Thief

May 17, 2016
Long after our own plain yellow sun expands to become a red giant star

Is that accurate? I would say, "M class star". It's not going to be much of a giant, no?

May 18, 2016
"Hunting for hidden life on worlds orbiting old, red stars."

This can be named with one word: Desperation
Huh. I think desperation would be giving up looking for new things, and falling back on some phony feelgood superstition, just because its a whole lot less scarier and a whole lot easier to do so.

May 22, 2016
That can be named with one word: Trolling.

Desperation is a troll that attacks a productive science for an achievement. The achievement has added to humanity; the troll has detracted.

@jljenkins: Technically all stars that get off the main sequence (being a regular star) in that manner is a "red giant"- Admittedly, not as large as other giants. https://en.wikipe...t_branch

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