Starship Asterisk*

Ann wrote: ↑Sun Dec 15, 2019 5:04 am

Chris Peterson wrote: ↑Sat Dec 14, 2019 5:50 pm

Ann wrote: ↑Sat Dec 14, 2019 7:26 am :bang: False color APOD! :bang:

To be clear, this is not a false color image. It is a pseudocolor image- the source data is single channel (grayscale), with the original intensity values replaced with color values. This is done because it allows us to see and interpret more structure than we can do using intensity alone. Many different pseudocolor mappings are used to enhance structural details that would otherwise not be apparent.

Well, the term used to be false color. I like it. Anyway, the Hubble people could have said that it was a false (or pseudo) color image. They could have said that the image of the comet and the galaxy was processed to show these objects as differently colored. And they could have said that the comet was really much fainter than the galaxy. And they could have named the filter they used for the images.

Ann wrote: ↑Sun Dec 15, 2019 5:17 am

Chris Peterson wrote: ↑Sat Dec 14, 2019 8:34 pm

BDanielMayfield wrote: ↑Sat Dec 14, 2019 8:30 pm

Is that fact significant? That is, is it saying this comet differs somehow from local comets? Or is it just that it isn't passing close enough to the Sun for any ionization to occur?

No, not particularly significant for a small comet with a 2 AU perihelion. Not all comets show an obvious ion trail. It's likely most active comets have them, but that doesn't mean they'll be bright enough to detect. The dust trail is generally a lot brighter.

Wikipedia calls the cometary tails tails. But it does say (in the caption under the first picture) that a comet's antitail can be call a dust trail.

neufer wrote: ↑Sun Dec 15, 2019 2:18 pm

BDanielMayfield wrote: ↑Sun Dec 15, 2019 1:45 pm

RocketRon wrote: ↑Sun Dec 15, 2019 5:06 am
So, will we be ready to put a probe onto a future visitor, to analyse what its made of.

Now that could be interesting ??

This may require more than a few days notice, of course.....

That would require better rockets, RocketRon. Or more likely, some propulsion system(s) that is better than rockets at supplying high delta V. Interstellar visitors will always be moving faster than objects bound to our system, so they will be harder to catch.

• Smaller payloads and better detection systems (no offense Borisov) will soon make this a reality:

https://en.wikipedia.org/wiki/2I/Borisov#Exploration wrote:
<<The higher hyperbolic excess velocity of 2I/Borisov of 32 km/s makes it even harder to reach for a spacecraft than 1I/'Oumuamua (26 km/s). According to a team of the Initiative for Interstellar Studies, a two-ton spacecraft could theoretically have been sent in July 2018 to intercept 2I/Borisov using a Falcon Heavy-class launcher, but only if the object had been discovered much earlier than it was. Launches after the actual discovery date would require a significantly larger launcher such as the Space Launch System (SLS) and Oberth manoeuvres near Jupiter and near the Sun. By September 2019, even an SLS-class launcher would only be able to deliver a 3 kg payload (such as a CubeSat) into a trajectory that could intercept 2I/Borisov in 2045 at a relative speed of 34 km/s. According to congressional testimony, NASA may need at least five years of preparation to launch such an intercepting mission.>>

BDanielMayfield wrote: ↑Sun Dec 15, 2019 3:35 pm One interesting suggestion has been to preposition an interceptor in space, having it wait somewhere in (a solar?) orbit until a suitable interstellar object arrives. Probably would need more than one to increase odds of favorable positioning. Expensive, but doable.

Chris Peterson wrote: ↑Sun Dec 15, 2019 3:53 pm

BDanielMayfield wrote: ↑Sun Dec 15, 2019 3:35 pm One interesting suggestion has been to preposition an interceptor in space, having it wait somewhere in (a solar?) orbit until a suitable interstellar object arrives. Probably would need more than one to increase odds of favorable positioning. Expensive, but doable.

Not clear this would provide any advantage. We already have a launch platform in orbit around the Sun. It's called Earth.

BDanielMayfield wrote: ↑Sun Dec 15, 2019 7:58 pm

Chris Peterson wrote: ↑Sun Dec 15, 2019 3:53 pm

BDanielMayfield wrote: ↑Sun Dec 15, 2019 3:35 pm One interesting suggestion has been to preposition an interceptor in space, having it wait somewhere in (a solar?) orbit until a suitable interstellar object arrives. Probably would need more than one to increase odds of favorable positioning. Expensive, but doable.

Not clear this would provide any advantage. We already have a launch platform in orbit around the Sun. It's called Earth.

Well of course, but the advantage would be already being outside Earth's gravity well. Also it would be possible to dock more than one stage lifted up from Earth separately. Then point and fire quickly when a catchable target shows up, probably including a gravity assist flyby or two also.

I'm not suggesting that such a scheme is all that practical (given costs, etc.), just that it could be possible.

Chris Peterson wrote: ↑Sun Dec 15, 2019 8:05 pm

BDanielMayfield wrote: ↑Sun Dec 15, 2019 7:58 pm

Chris Peterson wrote: ↑Sun Dec 15, 2019 3:53 pm
We already have a launch platform in orbit around the Sun. It's called Earth.

Well of course, but the advantage would be already being outside Earth's gravity well. Also it would be possible to dock more than one stage lifted up from Earth separately. Then point and fire quickly when a catchable target shows up, probably including a gravity assist flyby or two also. I'm not suggesting that such a scheme is all that practical (given costs, etc.), just that it could be possible.

Getting out of Earth's gravity well is a small task compared with matching velocities between a probe and an arbitrary object in the Solar System.

• 1) there are no weather delays or air drag in space and
  
  2) one can always thrust in the ongoing direction of travel
  • & perpendicular to gravity.
  .........................................................................
  The Saturn V had a thrust of 7,891,000 lb
  but, at first, most of that thrust was was used up
  simply in levitating an initial mass of 6,540,000 lb.

https://en.wikipedia.org/wiki/Falcon_Heavy wrote:

Code: Select all

Falcon Heavy                 1,420,788 kg
Payload to GTO                  26,700 kg
Payload to Mars                 16,800 kg
Payload to Pluto                 3,500 kg

neufer wrote: ↑Sun Dec 15, 2019 11:17 pm The probe needn't match velocities with an interstellar interloper but merely intercept it.

Bruce's concept makes use of at least 2 space thrust advantages:
.........................................................................

• 1) there are no weather delays or air drag in space and
  
  2) one can always thrust in the ongoing direction of travel
  • & perpendicular to gravity.

Chris Peterson wrote: ↑Sun Dec 15, 2019 11:30 pm
Number (2) is a minor advantage, but has to be offset against the much larger cost associated with placing a long lived (several years, at least) probe into a stable orbit, carrying a lot of fuel, when whatever orbit is chosen is statistically unlikely to provide a better launch opportunity than the Earth (any interstellar visitor will be on a random inclination). I imagine we could launch quite a few fast interceptors from Earth for the cost of a single space-based mission. Which might expire before even being used.

neufer wrote: ↑Mon Dec 16, 2019 12:43 am

Chris Peterson wrote: ↑Sun Dec 15, 2019 11:30 pm
Number (2) is a minor advantage, but has to be offset against the much larger cost associated with placing a long lived (several years, at least) probe into a stable orbit, carrying a lot of fuel, when whatever orbit is chosen is statistically unlikely to provide a better launch opportunity than the Earth (any interstellar visitor will be on a random inclination). I imagine we could launch quite a few fast interceptors from Earth for the cost of a single space-based mission. Which might expire before even being used.

Maintaining "a long lived (several years, at least) probe in a stable orbit, carrying a lot of fuel" is a lot easier than maintaining a large rocket that is ready to go on short notice sitting on the ground for several years. Multiple probes in different elliptical geosynchronous orbits could be optimized to assure that one of them had the best chance to intercept any random interstellar interloper orbit.

(The fickle political will to maintain large rockets sitting on the ground might expire before they are even used.)

TheOtherBruce wrote: ↑Mon Dec 16, 2019 1:12 pm
Could this be its first close solar encounter, or has it been through the broiler before?

TheOtherBruce wrote: ↑Mon Dec 16, 2019 1:12 pm Okay, now that we have a confirmed interstellar comet, there are a few questions that have intrigued me; what sort of system could it have come from? Was it ejected from its original system very early, during planetary migration, or is it older? Could this be its first close solar encounter, or has it been through the broiler before?

https://www.nasa.gov/feature/goddard/2022/studying-the-next-interstellar-interloper-with-webb wrote:
Studying the Next Interstellar Interloper with Webb
Feb 16, 2022

<<One of the most exciting findings in planetary science in recent years is the discovery of interstellar objects passing through our solar system. So far, astronomers have confirmed only two of these interlopers from other star systems — 1I/'Oumuamua in 2017 and 2I/Borisov in 2018 — but many, many more are thought to exist. Scientists have had only limited ability to study these objects once discovered, but all of that is about to change with NASA's James Webb Space Telescope. "The supreme sensitivity and power of Webb now present us with an unprecedented opportunity to investigate the chemical composition of these interstellar objects and find out so much more about their nature: where they come from, how they were made, and what they can tell us about the conditions present in their home systems," explained Martin Cordiner, principal investigator of a Webb Target of Opportunity program to study the composition of an interstellar object. "The ability to study one of these and find out its composition — to really see material from around another planetary system close up — is truly an amazing thing," said Cordiner, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and The Catholic University of America. The first two interstellar objects detected were very different: One was very comet-like, and one was not. Cordiner and his team hope to find out how unique those objects were and whether they're representative of the broader population of interstellar objects.

Astronomers are constantly monitoring various sources of information ranging from amateur observers to professional observatories in the hopes of finding the next interstellar interloper. When the next such object is first detected, scientists won't immediately be certain if it's an interstellar object. They'll need additional observations over a period of days, weeks, or even months to confirm it — depending on its brightness. Once they have confirmation that the object came from outside the solar system based on its "hyperbolic" orbit, and they are certain the object didn't come from the outer reaches of our own solar system or the Oort cloud, they can calculate the trajectory of the object across the sky. If that trajectory intersects with Webb's viewing field, Cordiner and his team will make the observations. The team will use Webb's spectroscopic capabilities in both the near-infrared and mid-infrared bands to study two different aspects of the interstellar object. First, using the Near-Infrared Spectrograph (NIRSpec), they will analyze the chemical fingerprints of gases released by the object as any ices that might be present are vaporized by our Sun's heat. Second, with the Mid-Infrared Instrument (MIRI), they will observe any dust that the object is producing — small, microscopic particles; larger grains; and even pebbles that may be lifted off the surface and surrounding the object. With its high spectral resolution, NIRSpec can pick out the emission from individual gases, allowing the team to detect specific molecules such as water, methanol, formaldehyde, carbon dioxide, carbon monoxide, and methane. MIRI, in the mid-infrared, is more tuned to the heat spectrum produced by solid particles, such as dust grains or the object's nucleus.

In our own solar system, comets are icy remnants from the era of planet formation around our Sun, so they can provide unique insight into the chemical conditions present in the earliest history of our solar system. This Webb program has the ability to reveal — for the first time — similarly powerful insights into the chemistry of the formation of planets around other stars. Astronomers don't fully understand the exact chemical processes involved in forming planets. For example, how does a planet arise from simple chemical ingredients? Does it happen in the same way around all stars? Was there anything peculiar about the way our own planets formed around our Sun, compared with how they form around other stars elsewhere in the galaxy? If scientists can get proof of the chemical conditions present in other planetary systems by observing an interstellar object and seeing what it's made of, then they can get a much clearer picture of the true extent of chemistry that's possible in those other planetary systems. Interstellar objects have not been observed before in these important near- and mid-infrared wavelength ranges, so the possibilities for new discoveries are quite profound. With trillions and trillions of interstellar objects buzzing around the galaxy, the team doesn't know what they are going to find, but they know that it will be fascinating. "With Webb, we can do really interesting science at much fainter magnitudes or brightnesses," explained teammate Cristina Thomas, an assistant professor of astronomy at Northern Arizona University. "Also, we've never been able to observe interstellar objects in this region of the infrared. It opens a lot of opportunities for the different compositional signatures that we're interested in. That's going to be a huge boon for us!">>