APOD: The Kepler-90 Planetary System (2020 Apr 28)

[APOD Robot]

The Kepler-90 Planetary System

Explanation: Do other stars have planetary systems like our own? Yes -- one such system is Kepler-90. Cataloged by the Kepler satellite that operated from Earth orbit between 2009 and 2018, eight planets were discovered, giving Kepler-90 the same number of known planets as our Solar System. Similarities between Kepler-90 and our system include a G-type star comparable to our Sun, rocky planets comparable to our Earth, and large planets comparable in size to Jupiter and Saturn. Differences include that all of the known Kepler-90 planets orbit relatively close in -- closer than Earth's orbit around the Sun -- making them possibly too hot to harbor life. However, observations over longer time periods may discover cooler planets further out. Kepler-90 lies about 2,500 light years away, and at magnitude 14 is visible with a medium-sized telescope toward the constellation of the Dragon (Draco). The exoplanet-finding mission TESS was launched in 2018, while missions with exoplanet finding capability planned for launch in the next decade include NASA's JWST and WFIRST.

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[isoparix]

I'm surprised you can pack eight large planets stably within an eath orbit. If eight is possible, what's the maximum?!!!

[orin stepanek]

I think these planets a little far out for my liking !

[Orange Sky]

And what a sight the night sky must offer. Instead of a train of starlinks, a train of planets ….

[sillyworm 2]

So frustrating to read about how long it would take to reach some of the known exoplanets.Even at impossible light speeds they are still realistically just too far away.A probe would take a dauntingly long time.Such a tease.

[Chris Peterson]

So frustrating to read about how long it would take to reach some of the known exoplanets.Even at impossible light speeds they are still realistically just too far away.A probe would take a dauntingly long time.Such a tease.

There is no limit on how fast you could reach another star. You could do it in a day with the right ship. The only problem is that you'd have no way to communicate your findings with anybody back home, except delayed by years or centuries or millennia.

[xiaoyu Mu]

its true those planets are far away from our homeland, but its true that we humanbeings are approching to get close to them

[sillyworm 2]

Chris, One can only wish and hope.One of the exoplanets I researched would take a ship,at light speed,734,000 years.

[Chris Peterson]

Chris, One can only wish and hope.One of the exoplanets I researched would take a ship,at light speed,734,000 years.

The point is, the amount of time it takes from the perspective of those on the ship can be arbitrarily short. It may take a ship 734,000 years to reach another star from the perspective of those on Earth, but it could take just hours from the perspective of those on the ship. Welcome to special relativity!

[sillyworm 2]

Do we even have a clue as to what it may take to even start to understand this spaceship travel concept? I know lots if things look good on paper.What is the most advanced realistic idea?

[Chris Peterson]

Do we even have a clue as to what it may take to even start to understand this spaceship travel concept? I know lots if things look good on paper.What is the most advanced realistic idea?

The technology is far beyond anything we have. But it's important to recognize that it's fundamentally an engineering problem, not any problem imposed by natural laws or science that remains beyond our understanding.

[Ann]

Chris, One can only wish and hope.One of the exoplanets I researched would take a ship,at light speed,734,000 years.

The point is, the amount of time it takes from the perspective of those on the ship can be arbitrarily short. It may take a ship 734,000 years to reach another star from the perspective of those on Earth, but it could take just hours from the perspective of those on the ship. Welcome to special relativity!

I understand the concept of time dilation, but I have a number of questions nevertheless. In order to achieve significant time dilation and make the journey reasonably short, it will be necessary to accelerate the ship to high speeds. Clearly the time of acceleration can't be arbitrarily short, because the human body wouldn't be able to tolerate it. Or perhaps you mean, Chris, that no humans would be on board this ship, only machines?

It has been proposed that it would be possible to build huge cosmic "sailing vessels" that would use, among other things, the solar wind to accelerate. Clearly this sort of acceleration would be very slow, and it seems to me that it would take far more than a human lifetime to gain enough acceleration to clear the Solar system by this means.

In order to gain reasonable acceleration, it would be necessary to bring, I would think, huge amounts of fuel. Or do we foresee the invention of "dilithium crystals" similar to the kind they use in Star Trek, that can accelerate a ship quickly and easily to speeds faster than light?

In order to achieve significant time dilation, it would be necessary to move at a significant fraction of the speed of light. But space isn't empty. Colliding with high energy cosmic particles at a significant fraction of the speed of light, and colliding with dust particles and tiny particles of cosmic debris, would in all probability be very bad for the integrity of the spaceship. How do we protect the ship from turning into a spaceship variety of Swiss cheese because of all the collisions with "cosmic grains of sand"? 🡰

Any thoughts about this, Chris?

Ann

[neufer]

---

It may take a ship 734,000 years to reach another star from the perspective of those on Earth, but it could take just hours from the perspective of those on the ship. Welcome to special relativity!

In order to achieve significant time dilation and make the journey reasonably short, it will be necessary to accelerate the ship to high speeds. Clearly the time of acceleration can't be arbitrarily short, because the human body wouldn't be able to tolerate it.

<<At a constant acceleration of 1 g, a rocket could travel the diameter of our galaxy in about 12 years ship time, and about 113,000 years planetary time. If the last half of the trip involves deceleration at 1 g, the trip would take about 24 years..and a round trip time of about 48 years.>>

[Chris Peterson]

Chris, One can only wish and hope.One of the exoplanets I researched would take a ship,at light speed,734,000 years.

The point is, the amount of time it takes from the perspective of those on the ship can be arbitrarily short. It may take a ship 734,000 years to reach another star from the perspective of those on Earth, but it could take just hours from the perspective of those on the ship. Welcome to special relativity!

I understand the concept of time dilation, but I have a number of questions nevertheless. In order to achieve significant time dilation and make the journey reasonably short, it will be necessary to accelerate the ship to high speeds. Clearly the time of acceleration can't be arbitrarily short, because the human body wouldn't be able to tolerate it. Or perhaps you mean, Chris, that no humans would be on board this ship, only machines?

Certainly there are practical limits on acceleration set by human physiology. The greater the distance you travel, however, the greater the benefit from time dilation and constant acceleration. At 1G, it would take 4 years to travel 4 light years (half of the time accelerating at 1G, half of the time decelerating at 1G). At 2G, it would take 2.8 years. Humans might be able to deal with 2G for that long... or not. But suppose you want to go 100 ly? At 1G, you can do that in just 19 years (again, acceleration then deceleration). 19 years ship time, over 100 years Earth time.

It has been proposed that it would be possible to build huge cosmic "sailing vessels" that would use, among other things, the solar wind to accelerate. Clearly this sort of acceleration would be very slow, and it seems to me that it would take far more than a human lifetime to gain enough acceleration to clear the Solar system by this means.

Yeah. Not a method to use if you want to get somewhere fast.

In order to gain reasonable acceleration, it would be necessary to bring, I would think, huge amounts of fuel. Or do we foresee the invention of "dilithium crystals" similar to the kind they use in Star Trek, that can accelerate a ship quickly and easily to speeds faster than light?

The amount of energy is large, but not in comparison to what is theoretically possible if you could efficiently convert mass to energy according to E=mc². This is an engineering problem, not a fundamental science problem.

In order to achieve significant time dilation, it would be necessary to move at a significant fraction of the speed of light. But space isn't empty. Colliding with high energy cosmic particles at a significant fraction of the speed of light, and colliding with dust particles and tiny particles of cosmic debris, would in all probability be very bad for the integrity of the spaceship. How do we protect the ship from turning into a spaceship variety of Swiss cheese because of all the collisions with "cosmic grains of sand"?

A serious problem. But again, an engineering problem more than anything.

[Ann]

The point is, the amount of time it takes from the perspective of those on the ship can be arbitrarily short. It may take a ship 734,000 years to reach another star from the perspective of those on Earth, but it could take just hours from the perspective of those on the ship. Welcome to special relativity!

I understand the concept of time dilation, but I have a number of questions nevertheless. In order to achieve significant time dilation and make the journey reasonably short, it will be necessary to accelerate the ship to high speeds. Clearly the time of acceleration can't be arbitrarily short, because the human body wouldn't be able to tolerate it. Or perhaps you mean, Chris, that no humans would be on board this ship, only machines?

Certainly there are practical limits on acceleration set by human physiology. The greater the distance you travel, however, the greater the benefit from time dilation and constant acceleration. At 1G, it would take 4 years to travel 4 light years (half of the time accelerating at 1G, half of the time decelerating at 1G). At 2G, it would take 2.8 years. Humans might be able to deal with 2G for that long... or not. But suppose you want to go 100 ly? At 1G, you can do that in just 19 years (again, acceleration then deceleration). 19 years ship time, over 100 years Earth time.

It has been proposed that it would be possible to build huge cosmic "sailing vessels" that would use, among other things, the solar wind to accelerate. Clearly this sort of acceleration would be very slow, and it seems to me that it would take far more than a human lifetime to gain enough acceleration to clear the Solar system by this means.

Yeah. Not a method to use if you want to get somewhere fast.

In order to gain reasonable acceleration, it would be necessary to bring, I would think, huge amounts of fuel. Or do we foresee the invention of "dilithium crystals" similar to the kind they use in Star Trek, that can accelerate a ship quickly and easily to speeds faster than light?

The amount of energy is large, but not in comparison to what is theoretically possible if you could efficiently convert mass to energy according to E=mc². This is an engineering problem, not a fundamental science problem.

In order to achieve significant time dilation, it would be necessary to move at a significant fraction of the speed of light. But space isn't empty. Colliding with high energy cosmic particles at a significant fraction of the speed of light, and colliding with dust particles and tiny particles of cosmic debris, would in all probability be very bad for the integrity of the spaceship. How do we protect the ship from turning into a spaceship variety of Swiss cheese because of all the collisions with "cosmic grains of sand"?

A serious problem. But again, an engineering problem more than anything.

Thanks for your answers, Chris! And thank you, in particular, for telling a mathematically challenged person like myself how long it would take to travel 100 light-years in space, while accelerating constantly at 1G... 19 years ship time! I was impressed!

But I couldn't help chuckling when you said that overcoming most of the difficulties of deep-space space flight is just an engineering problem. I am the owner of a book called Beyond the Solar System, written by Willy Ley, illustrated by Chesley Bonestell, and with a foreword by Wernher von Braun, printed in 1964. In the foreword, Willy Leigh talked about sending a manned expedition to Alpha Centauri. Several times in the book Willy Leigh said that we don't yet know how to travel far outside the Solar system, but that is just an engineering problem, and it is for our engineers to figure out.

Willy Leigh wrote about the first manned expedition to Alpha Centauri:

I think that such an expedition will be made at a time when people now alive (though very young) will be able to watch the take-off on television- say, half a century from now.

And since the book was printed in 1964, I have to assume that Willy Leigh was saying that the take-off of the first manned expedition to Alpha Centauri would take place in about 2014. I guess we're running a bit late.

Ann

[Ann]

---

It may take a ship 734,000 years to reach another star from the perspective of those on Earth, but it could take just hours from the perspective of those on the ship. Welcome to special relativity!

In order to achieve significant time dilation and make the journey reasonably short, it will be necessary to accelerate the ship to high speeds. Clearly the time of acceleration can't be arbitrarily short, because the human body wouldn't be able to tolerate it.

<<At a constant acceleration of 1 g, a rocket could travel the diameter of our galaxy in about 12 years ship time, and about 113,000 years planetary time. If the last half of the trip involves deceleration at 1 g, the trip would take about 24 years..and a round trip time of about 48 years.>>

Thank you, too, Art, for your answer. Very interesting.

Ann

[Chris Peterson]

But I couldn't help chuckling when you said that overcoming most of the difficulties of deep-space space flight is just an engineering problem.

It's sort of funny, but it's also a useful concept. I happen to think that our understanding of the fundamental laws of nature is nearly complete- just a few holes left to fill. I imagine in a century we'll know every law of physics. But there's a huge step between knowing the fundamental laws and figuring out all the things you can actually do with them. Just look around at all the new inventions that show up every year. Every day. Virtually none employ science less than decades old. But it still took a long time to get there. Technology is much slower than scientific knowledge.

I imagine that if we were to encounter an ancient technological species, say a million years old, their understanding of nature and the Universe would be almost the same as ours. But their technology would be, well, a million years more advanced.

[sillyworm 2]

Stepping back a few paces..I'll be quite happy when we start to get some data from the James Webb Space Telescope.Feet back on the ground...for now.

[neufer]

---

But I couldn't help chuckling when you said that overcoming most of the difficulties of deep-space space flight is just an engineering problem.

It's sort of funny, but it's also a useful concept.

One is still limited by the ideal rocket equation:

Click to view full size image

where the effective (photon) exhaust velocity v_e= c.

Essentially, the initial spaceship must have a
MASS₀ that is ~ exp(T_t) x final (payload) spaceship mass_f
where T_t = the total number of traveler years
spent at 1-Gee acceleration/deceleration.

Ergo: 1-Gee trips longer than a decade are prohibited on practical grounds.

[Chris Peterson]

---

But I couldn't help chuckling when you said that overcoming most of the difficulties of deep-space space flight is just an engineering problem.

It's sort of funny, but it's also a useful concept.

One is still limited by the ideal rocket equation:

Click to view full size image

where the effective (photon) exhaust velocity v_e= c.

Essentially, the initial spaceship must have a
MASS₀ that is ~ exp(T_t) x final (payload) spaceship mass_f
where T_t = the total number of traveler years
spent at 1-Gee acceleration/deceleration.

Ergo: 1-Gee trips longer than a decade are prohibited on practical grounds.

This assumes, of course, that you can't collect more reaction mass along the way. Another engineering problem?

[sillyworm 2]

Prohibited because of undesirable outcomes? Or outcomes unknown? Or just because?

[Chris Peterson]

Prohibited because of undesirable outcomes? Or outcomes unknown? Or just because?

Prohibited by physics, given that you can't expel reaction mass at greater than c.

[neufer]

This assumes, of course, that you can't collect more reaction mass along the way.
Another engineering problem?

Particles, photons and magnetic fields in the way simply complicate the issue
...especially after the spacecraft becomes relativistic

[Chris Peterson]

This assumes, of course, that you can't collect more reaction mass along the way.
Another engineering problem?

Particles, photons and magnetic fields in the way simply complicate the issue
...especially after the spacecraft becomes relativistic

I didn't say it was a simple engineering problem!

[isoparix]

All very entertaining - but all very off-topic, if I may say so. I still want to know how you pack eight Jupiters stably, in between Earth and Mercury....