Scientists think our Solar System is unlikely combo to host life

Well, they talk about all kinds of variables such as the Sun's magnetic
field and the Earth's magnetic field. They mention a lot of stuff that
has already been discussed in these forums in the past, such as the
requirement that an Earth-like planet have a magnetic field to protect
its atmosphere against depletion by stellar winds. They also mention
that it would be more likely that a planet more massive than the Earth
is more likely to host life than Earth is, which has also been discussed
here that Earth is probably at the lowest end of the mass scale for a
life-bearing world.

They think a more likely combo is a K-class orange dwarf paired with a
Super-Earth of 2-3x Earth mass. In about a million years we'll be able
to see one of those up close, as Gliese 710 will come to within 1
light-year of us and become our closest stellar neighbour.

One interesting thing mentioned is that at birth the Sun was rotating 10
times faster than it is today. Therefore it had much larger magnetic
fields and more UV production. Any idea why the Sun slowed down over the
years? How did it lose its angular momentum?

Yousuf Khan

Sun, Earth Are Unlikely Pair to Support Life | Universe Today
"Edward Guinan, a professor of astronomy and astrophysics at Villanova
University in Pennsylvania, and his collaegues have been studying
Sun-like stars as windows into the origin of life on Earth, and as
indicators of how likely life is elsewhere in the cosmos. The work has
revealed that the Sun rotated more than ten times faster in its youth
(over four billion years ago) than today. The faster a star rotates, the
harder the magnetic dynamo at its core works, generating a stronger
magnetic field, so the young Sun emitted X-rays and ultraviolet
radiation up to several hundred times stronger than it does today."
http://www.universetoday.com/2009/08...-support-life/

On Aug 10, 3:49*pm, Yousuf Khan wrote:
Well, they talk about all kinds of variables such as the Sun's magnetic
field and the Earth's magnetic field. They mention a lot of stuff that
has already been discussed in these forums in the past, such as the
requirement that an Earth-like planet have a magnetic field to protect
its atmosphere against depletion by stellar winds. They also mention
that it would be more likely that a planet more massive than the Earth
is more likely to host life than Earth is, which has also been discussed
here that Earth is probably at the lowest end of the mass scale for a
life-bearing world.

They think a more likely combo is a K-class orange dwarf paired with a
Super-Earth of 2-3x Earth mass. In about a million years we'll be able
to see one of those up close, as Gliese 710 will come to within 1
light-year of us and become our closest stellar neighbour.

One interesting thing mentioned is that at birth the Sun was rotating 10
times faster than it is today. Therefore it had much larger magnetic
fields and more UV production. Any idea why the Sun slowed down over the
years? How did it lose its angular momentum?

Rotation speed is conserved. Spin can increase but rotation cannot
decrease.

Mitch Raemsch

* * * * Yousuf Khan

Sun, Earth Are Unlikely Pair to Support Life | Universe Today
"Edward Guinan, a professor of astronomy and astrophysics at Villanova
University in Pennsylvania, and his collaegues have been studying
Sun-like stars as windows into the origin of life on Earth, and as
indicators of how likely life is elsewhere in the cosmos. The work has
revealed that the Sun rotated more than ten times faster in its youth
(over four billion years ago) than today. The faster a star rotates, the
harder the magnetic dynamo at its core works, generating a stronger
magnetic field, so the young Sun emitted X-rays and ultraviolet
radiation up to several hundred times stronger than it does today."http://www.universetoday.com/2009/08/10/sun-earth-are-unlikely-pair-t...

In article ,
Yousuf Khan writes:
One interesting thing mentioned is that at birth the Sun was rotating 10
times faster than it is today. Therefore it had much larger magnetic
fields and more UV production. Any idea why the Sun slowed down over the
years? How did it lose its angular momentum?

One idea that used to be popular was magnetic coupling to an
accretion disk. I don't know whether or not this hypothesis is still
current. Rotation of solar-type stars shows a negative correlation
with age, so there is pretty good evidence it slows down somehow.
(Unless more recent observations have changed the picture -- I'm at
least a few years out of date on this subject.)

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

Steve Willner wrote:
In article ,
Yousuf Khan writes:
One interesting thing mentioned is that at birth the Sun was rotating 10
times faster than it is today. Therefore it had much larger magnetic
fields and more UV production. Any idea why the Sun slowed down over the
years? How did it lose its angular momentum?

One idea that used to be popular was magnetic coupling to an
accretion disk. I don't know whether or not this hypothesis is still
current. Rotation of solar-type stars shows a negative correlation
with age, so there is pretty good evidence it slows down somehow.
(Unless more recent observations have changed the picture -- I'm at
least a few years out of date on this subject.)



Wouldn't the period of slowdown then have ended pretty much when the
accretion disk disappeared?

If old stars are slowing down with age, then there must be a friction
source within its own solar system. Such things as planets exerting
tidal forces on their star? During that time if the planets are slowing
down their sun, then they must be gaining energy and getting farther out
in their orbits.

Yousuf Khan

On Aug 10, 4:49*pm, Yousuf Khan wrote:
Well, they talk about all kinds of variables such as the Sun's magnetic
field and the Earth's magnetic field. They mention a lot of stuff that
has already been discussed in these forums in the past, such as the
requirement that an Earth-like planet have a magnetic field to protect
its atmosphere against depletion by stellar winds. They also mention
that it would be more likely that a planet more massive than the Earth
is more likely to host life than Earth is, which has also been discussed
here that Earth is probably at the lowest end of the mass scale for a
life-bearing world.

They think a more likely combo is a K-class orange dwarf paired with a
Super-Earth of 2-3x Earth mass. In about a million years we'll be able
to see one of those up close, as Gliese 710 will come to within 1
light-year of us and become our closest stellar neighbour.

One interesting thing mentioned is that at birth the Sun was rotating 10
times faster than it is today. Therefore it had much larger magnetic
fields and more UV production. Any idea why the Sun slowed down over the
years? How did it lose its angular momentum?

* * * * Yousuf Khan

Sun, Earth Are Unlikely Pair to Support Life | Universe Today
"Edward Guinan, a professor of astronomy and astrophysics at Villanova
University in Pennsylvania, and his collaegues have been studying
Sun-like stars as windows into the origin of life on Earth, and as
indicators of how likely life is elsewhere in the cosmos. The work has
revealed that the Sun rotated more than ten times faster in its youth
(over four billion years ago) than today. The faster a star rotates, the
harder the magnetic dynamo at its core works, generating a stronger
magnetic field, so the young Sun emitted X-rays and ultraviolet
radiation up to several hundred times stronger than it does today."http://www.universetoday.com/2009/08/10/sun-earth-are-unlikely-pair-t...

Why are you still excluding the Sirius star/solar system?

Are we going to go blind if we look at Sirius A?

~ BG

On Aug 12, 8:53*pm, Yousuf Khan wrote:
Steve Willner wrote:
In article ,
*Yousuf Khan writes:
One interesting thing mentioned is that at birth the Sun was rotating 10
times faster than it is today. Therefore it had much larger magnetic
fields and more UV production. Any idea why the Sun slowed down over the
years? How did it lose its angular momentum?

One idea that used to be popular was magnetic coupling to an
accretion disk. *I don't know whether or not this hypothesis is still
current. *Rotation of solar-type stars shows a negative correlation
with age, so there is pretty good evidence it slows down somehow.
(Unless more recent observations have changed the picture -- I'm at
least a few years out of date on this subject.)

Wouldn't the period of slowdown then have ended pretty much when the
accretion disk disappeared?

If old stars are slowing down with age, then there must be a friction
source within its own solar system. Such things as planets exerting
tidal forces on their star? During that time if the planets are slowing
down their sun, then they must be gaining energy and getting farther out
* in their orbits.

* * * * Yousuf Khan

It just doesn't add up, does it.

~ BG

SW Rotation of solar-type stars shows a negative correlation
SW with age,

In article ,
Yousuf Khan writes:
If old stars are slowing down with age, then there must be a friction
source within its own solar system.

Yes, of course. The correlation I mentioned holds (or did, last time
I heard about it) only for young stars, which might still have
disks. But as I wrote before, I'm several years out of date on this,
and I expect a lot more is known now. Anybody want to chime in with
an update?

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA