How Astronomers Missed the Massive Asteroid That Just Whizze

[Steve Wilson]

July 26, 2019

How Astronomers Missed the Massive Asteroid That Just Whizzed Past Earth

By Yasemin Saplakoglu, Staff Writer

A large asteroid just whizzed past our planet - and astronomers
weren't expecting it.

Ranging in size from 187 to 427 feet (57 to 130 meters) wide, the
space rock named 2019 OK snuck up on us Thursday morning (July 25).

It swung as close as 45,000 miles (73,000 kilometers) from Earth,
what one astronomer told The Washington Post was "uncomfortably
close."

If the asteroid had actually collided with Earth, the crash would
have caused devastating damage.

For example, back in 2013, a meteor snuck up on us and exploded over
the Russian city of Chelyabinsk; that blast was stronger than a
nuclear explosion, and the resulting shock wave shattered glass down
below and injured more than 1,000 people. The Chelyabinsk meteor was
much smaller than 2019 OK, spanning about 66 feet (20 meters)
across.

NASA is tracking over 90 percent of the asteroids that are 0.62
miles (1 km) or larger and are orbiting close to our planet.

https://www.livescience.com/66043-giant-asteroid-flyby-surprises-
astronomers.html
----------------------------------------------------------------

Pleasant dreams

 

[bitrex]

On 7/29/19 11:23 AM, bitrex wrote:

On 7/28/19 8:21 PM, Steve Wilson wrote:
July 26, 2019

How Astronomers Missed the Massive Asteroid That Just Whizzed Past Earth

By Yasemin Saplakoglu, Staff Writer

A large asteroid just whizzed past our planet - and astronomers
weren't expecting it.

Ranging in size from 187 to 427 feet (57 to 130 meters) wide, the
space rock named 2019 OK snuck up on us Thursday morning (July 25).

It swung as close as 45,000 miles (73,000 kilometers) from Earth,
what one astronomer told The Washington Post was "uncomfortably
close."

If the asteroid had actually collided with Earth, the crash would
have caused devastating damage.

For example, back in 2013, a meteor snuck up on us and exploded over
the Russian city of Chelyabinsk; that blast was stronger than a
nuclear explosion, and the resulting shock wave shattered glass down
below and injured more than 1,000 people. The Chelyabinsk meteor was
much smaller than 2019 OK, spanning about 66 feet (20 meters)
across.

NASA is tracking over 90 percent of the asteroids that are 0.62
miles (1 km) or larger and are orbiting close to our planet.

https://www.livescience.com/66043-giant-asteroid-flyby-surprises-
astronomers.html
----------------------------------------------------------------

Pleasant dreams


Also the difference between a 187 foot wide rock entering at a shallow
angle and a 427 foot wide rock entering at 90 degrees is the first
breaks up high in the atmosphere and probably ends up not being that
much more destructive on the ground as compared to the Chelyabinsk
event, vs the second case it starts to break up, but most of the
fragments punch straight through to the ground still going 7 km/sec and
you get a 250 megaton ground blast and 4 mile diameter crater.

thankfully even in the worst case, latter case the chances of it
happening over a heavily populated area are less than 1%

The Chelyabinsk asteroid was a 10 year average asteroid, besides that
one and Tunguska, since the invention of motion picture recording
technology, probably another dozen have come in like that one and hit
the deep ocean or exploded over a totally unpopulated area and nobody
noticed.

It took a while to get "lucky" and have one explode over an area
populated enough and with enough modern motion picture recording devices
for lots of documentation of it. Chelyabinsk could have gotten real
unlucky and had a somewhat larger asteroid come in at a somewhat steeper
angle and it wouldn't have been the end of the world, but a really,
really bad day for poor Chelyabinsk.

 

[bitrex]

On 7/28/19 8:21 PM, Steve Wilson wrote:

July 26, 2019

How Astronomers Missed the Massive Asteroid That Just Whizzed Past Earth

By Yasemin Saplakoglu, Staff Writer

A large asteroid just whizzed past our planet - and astronomers
weren't expecting it.

Ranging in size from 187 to 427 feet (57 to 130 meters) wide, the
space rock named 2019 OK snuck up on us Thursday morning (July 25).

It swung as close as 45,000 miles (73,000 kilometers) from Earth,
what one astronomer told The Washington Post was "uncomfortably
close."

If the asteroid had actually collided with Earth, the crash would
have caused devastating damage.

For example, back in 2013, a meteor snuck up on us and exploded over
the Russian city of Chelyabinsk; that blast was stronger than a
nuclear explosion, and the resulting shock wave shattered glass down
below and injured more than 1,000 people. The Chelyabinsk meteor was
much smaller than 2019 OK, spanning about 66 feet (20 meters)
across.

NASA is tracking over 90 percent of the asteroids that are 0.62
miles (1 km) or larger and are orbiting close to our planet.

https://www.livescience.com/66043-giant-asteroid-flyby-surprises-
astronomers.html
----------------------------------------------------------------

Pleasant dreams

Also the difference between a 187 foot wide rock entering at a shallow
angle and a 427 foot wide rock entering at 90 degrees is the first
breaks up high in the atmosphere and probably ends up not being that
much more destructive on the ground as compared to the Chelyabinsk
event, vs the second case it starts to break up, but most of the
fragments punch straight through to the ground still going 7 km/sec and
you get a 250 megaton ground blast and 4 mile diameter crater.

thankfully even in the worst case, latter case the chances of it
happening over a heavily populated area are less than 1%

 

On Mon, 29 Jul 2019 00:21:56 GMT, Steve Wilson <no@spam.com> wrote:

July 26, 2019

How Astronomers Missed the Massive Asteroid That Just Whizzed Past Earth

By Yasemin Saplakoglu, Staff Writer

A large asteroid just whizzed past our planet - and astronomers
weren't expecting it.

Ranging in size from 187 to 427 feet (57 to 130 meters) wide, the
space rock named 2019 OK snuck up on us Thursday morning (July 25).

It swung as close as 45,000 miles (73,000 kilometers) from Earth,
what one astronomer told The Washington Post was "uncomfortably
close."

Some animation claim that the flyby occurred when the asteroid was
flying towards perihelion, i.e. it would come from the night side of
Earth and it should be easier to detect earlier.

However, if it had already passed perihelion and be on the way out it
would have approached the Earth from the day side of earth, making it
very hard to detect with ground based optical telescopes. A space
telescope at L1 Lagrange point would be needed to detect asteroids
approaching from the day side.

 

[bitrex]

On 7/29/19 12:42 PM, upsidedown@downunder.com wrote:

On Mon, 29 Jul 2019 00:21:56 GMT, Steve Wilson <no@spam.com> wrote:

July 26, 2019

How Astronomers Missed the Massive Asteroid That Just Whizzed Past Earth

By Yasemin Saplakoglu, Staff Writer

A large asteroid just whizzed past our planet - and astronomers
weren't expecting it.

Ranging in size from 187 to 427 feet (57 to 130 meters) wide, the
space rock named 2019 OK snuck up on us Thursday morning (July 25).

It swung as close as 45,000 miles (73,000 kilometers) from Earth,
what one astronomer told The Washington Post was "uncomfortably
close."

Some animation claim that the flyby occurred when the asteroid was
flying towards perihelion, i.e. it would come from the night side of
Earth and it should be easier to detect earlier.

However, if it had already passed perihelion and be on the way out it
would have approached the Earth from the day side of earth, making it
very hard to detect with ground based optical telescopes. A space
telescope at L1 Lagrange point would be needed to detect asteroids
approaching from the day side.

How much warning time would we be talking?

the headline says "massive" but asteroids at the lower end of that range
are small enough that if you could intercept exoatmospherically with a
ten, 20 megaton nuclear weapon at a couple hundred meters would vaporize
the bulk of it.

 

[bitrex]

On 7/30/19 10:13 AM, bitrex wrote:

On 7/29/19 12:42 PM, upsidedown@downunder.com wrote:
On Mon, 29 Jul 2019 00:21:56 GMT, Steve Wilson <no@spam.com> wrote:

July 26, 2019

How Astronomers Missed the Massive Asteroid That Just Whizzed Past Earth

By Yasemin Saplakoglu, Staff Writer

A large asteroid just whizzed past our planet - and astronomers
weren't expecting it.

Ranging in size from 187 to 427 feet (57 to 130 meters) wide, the
space rock named 2019 OK snuck up on us Thursday morning (July 25).

It swung as close as 45,000 miles (73,000 kilometers) from Earth,
what one astronomer told The Washington Post was "uncomfortably
close."

Some animation claim that the flyby occurred when the asteroid was
flying towards perihelion, i.e. it would come from the night side of
Earth and it should be easier to detect earlier.

However, if it had already passed perihelion and be on the way out it
would have approached the Earth from the day side of earth, making it
very hard to detect with ground based optical telescopes. A space
telescope at L1 Lagrange point would be needed to detect asteroids
approaching from the day side.


How much warning time would we be talking?

the headline says "massive" but asteroids at the lower end of that range
are small enough that if you could intercept exoatmospherically with a
ten, 20 megaton nuclear weapon at a couple hundred meters would vaporize
the bulk of it.

Sadly it'll probably take one of these 10 to 50-year average bitches
coming in a little larger and a little faster at a steeper angle and
air-blasting at 15,000 feet over Europe or the US somewhere, and killing
or injuring 50,000, people before anyone gets the motivation up to put
any L1 early warning satellite up to spot them

 

On Tue, 30 Jul 2019 10:13:01 -0400, bitrex <user@example.net> wrote:

On 7/29/19 12:42 PM, upsidedown@downunder.com wrote:
On Mon, 29 Jul 2019 00:21:56 GMT, Steve Wilson <no@spam.com> wrote:

July 26, 2019

How Astronomers Missed the Massive Asteroid That Just Whizzed Past Earth

By Yasemin Saplakoglu, Staff Writer

A large asteroid just whizzed past our planet - and astronomers
weren't expecting it.

Ranging in size from 187 to 427 feet (57 to 130 meters) wide, the
space rock named 2019 OK snuck up on us Thursday morning (July 25).

It swung as close as 45,000 miles (73,000 kilometers) from Earth,
what one astronomer told The Washington Post was "uncomfortably
close."

Some animation claim that the flyby occurred when the asteroid was
flying towards perihelion, i.e. it would come from the night side of
Earth and it should be easier to detect earlier.

However, if it had already passed perihelion and be on the way out it
would have approached the Earth from the day side of earth, making it
very hard to detect with ground based optical telescopes. A space
telescope at L1 Lagrange point would be needed to detect asteroids
approaching from the day side.


How much warning time would we be talking?

An Earth crossing asteroid is less than a year within Earth's orbit
and hence on the day side as seen from the Earth. During this time, it
would only be visible with a space telescope.

How long the asteroid stays within Earth's orbit depends on the
orbital eccentricity, i.e. how deep into the solar system it will fly,
does it cross the orbit of Venus or even the orbit of Mercury. Thus
the time can be just a month or two. Worst of all, in the shortest
case, the asteroid will approach nearly from the direction of he Sun.

Using the SOHO solar observatory (located at L1) has a camera pointing
towards the Sun, but blanking out the actual disk of the Sun. It has
detected a lot of small Sun gracing comets just prior to flying on to
the back side of the Sun. If they survive the encounter with the Sun,
they will move very fast away from the Sun, possibly crossing the
orbit of and potentially colliding with Earth.

The SOHO camera field of view is only a few degrees just showing the
immediate vicinity of the Sun. The asteroid hunter at L1 would have to
have a much wider field of view (up to 180 degrees) but blank out the
sun from the view.

the headline says "massive" but asteroids at the lower end of that range
are small enough that if you could intercept exoatmospherically with a
ten, 20 megaton nuclear weapon at a couple hundred meters would vaporize
the bulk of it.

 

[John Larkin]

On Mon, 29 Jul 2019 19:42:22 +0300, upsidedown@downunder.com wrote:

On Mon, 29 Jul 2019 00:21:56 GMT, Steve Wilson <no@spam.com> wrote:

July 26, 2019

How Astronomers Missed the Massive Asteroid That Just Whizzed Past Earth

By Yasemin Saplakoglu, Staff Writer

A large asteroid just whizzed past our planet - and astronomers
weren't expecting it.

Ranging in size from 187 to 427 feet (57 to 130 meters) wide, the
space rock named 2019 OK snuck up on us Thursday morning (July 25).

It swung as close as 45,000 miles (73,000 kilometers) from Earth,
what one astronomer told The Washington Post was "uncomfortably
close."

Some animation claim that the flyby occurred when the asteroid was
flying towards perihelion, i.e. it would come from the night side of
Earth and it should be easier to detect earlier.

However, if it had already passed perihelion and be on the way out it
would have approached the Earth from the day side of earth, making it
very hard to detect with ground based optical telescopes. A space
telescope at L1 Lagrange point would be needed to detect asteroids
approaching from the day side.

One (and basically the only) use for the ISS would be as a
staging/launch point for asteroid deflection missiles.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Martin Brown]

On 29/07/2019 17:42, upsidedown@downunder.com wrote:

On Mon, 29 Jul 2019 00:21:56 GMT, Steve Wilson <no@spam.com> wrote:

July 26, 2019

How Astronomers Missed the Massive Asteroid That Just Whizzed Past Earth

By Yasemin Saplakoglu, Staff Writer

A large asteroid just whizzed past our planet - and astronomers
weren't expecting it.

Ranging in size from 187 to 427 feet (57 to 130 meters) wide, the
space rock named 2019 OK snuck up on us Thursday morning (July 25).

It swung as close as 45,000 miles (73,000 kilometers) from Earth,
what one astronomer told The Washington Post was "uncomfortably
close."

Some animation claim that the flyby occurred when the asteroid was
flying towards perihelion, i.e. it would come from the night side of
Earth and it should be easier to detect earlier.

The big ones that sneak up on us are typically either very dark covered
in carbon soot like dust or coming from the direction of the sun so that
they are in the twilight sky until the last possible moment or both. I
am a bit surprised that the automatic searchers didn't get it a bit
sooner (so will they be). There is a protocol for Earth crossers with
suspected close approach or collision risk at the minor planets centre.

They need a series of at least three good observations separated by a
few hours to get an initial orbital solution that can then be refined as
more widely spaced observations become available.

However, if it had already passed perihelion and be on the way out it
would have approached the Earth from the day side of earth, making it
very hard to detect with ground based optical telescopes. A space
telescope at L1 Lagrange point would be needed to detect asteroids
approaching from the day side.

The survey instruments are pretty good now.

It has been quite a while since a human comet searcher beat one of the
automated systems. Hence the comets and asteroids they find just have
name of detection system a year and a designation code. A lot used to be
called Levy or Tanaka in the good old days of dedicated experts.

--
Regards,
Martin Brown

 

On Tue, 30 Jul 2019 22:51:24 +0100, Martin Brown
<'''newspam'''@nezumi.demon.co.uk> wrote:

On 29/07/2019 17:42, upsidedown@downunder.com wrote:
On Mon, 29 Jul 2019 00:21:56 GMT, Steve Wilson <no@spam.com> wrote:

July 26, 2019

How Astronomers Missed the Massive Asteroid That Just Whizzed Past Earth

By Yasemin Saplakoglu, Staff Writer

A large asteroid just whizzed past our planet - and astronomers
weren't expecting it.

Ranging in size from 187 to 427 feet (57 to 130 meters) wide, the
space rock named 2019 OK snuck up on us Thursday morning (July 25).

It swung as close as 45,000 miles (73,000 kilometers) from Earth,
what one astronomer told The Washington Post was "uncomfortably
close."

Some animation claim that the flyby occurred when the asteroid was
flying towards perihelion, i.e. it would come from the night side of
Earth and it should be easier to detect earlier.

The big ones that sneak up on us are typically either very dark covered
in carbon soot like dust or coming from the direction of the sun so that
they are in the twilight sky until the last possible moment or both. I
am a bit surprised that the automatic searchers didn't get it a bit
sooner (so will they be). There is a protocol for Earth crossers with
suspected close approach or collision risk at the minor planets centre.

A very dark carbon asteroid inside the orbit of the Earth will get
*hot* and radiate a lot in the 8-15 um thermal-IR range but very
little in the near-IR or visible range. Thus comparing ThIR and NIR
pictures should help identifying such objects.

Since the hot object is tumbling around it will also radiate ThIR on
the "night" side of the object, while a very reflective object nearly
on the line between Sun and Earth, will have a very small reflective
area for visible light and NIR.

 

[Martin Brown]

On 31/07/2019 07:20, upsidedown@downunder.com wrote:

On Tue, 30 Jul 2019 22:51:24 +0100, Martin Brown
'''newspam'''@nezumi.demon.co.uk> wrote:

On 29/07/2019 17:42, upsidedown@downunder.com wrote:
On Mon, 29 Jul 2019 00:21:56 GMT, Steve Wilson <no@spam.com> wrote:

July 26, 2019

How Astronomers Missed the Massive Asteroid That Just Whizzed Past Earth

By Yasemin Saplakoglu, Staff Writer

A large asteroid just whizzed past our planet - and astronomers
weren't expecting it.

Ranging in size from 187 to 427 feet (57 to 130 meters) wide, the
space rock named 2019 OK snuck up on us Thursday morning (July 25).

It swung as close as 45,000 miles (73,000 kilometers) from Earth,
what one astronomer told The Washington Post was "uncomfortably
close."

Some animation claim that the flyby occurred when the asteroid was
flying towards perihelion, i.e. it would come from the night side of
Earth and it should be easier to detect earlier.

The big ones that sneak up on us are typically either very dark covered
in carbon soot like dust or coming from the direction of the sun so that
they are in the twilight sky until the last possible moment or both. I
am a bit surprised that the automatic searchers didn't get it a bit
sooner (so will they be). There is a protocol for Earth crossers with
suspected close approach or collision risk at the minor planets centre.

A very dark carbon asteroid inside the orbit of the Earth will get
*hot* and radiate a lot in the 8-15 um thermal-IR range but very
little in the near-IR or visible range. Thus comparing ThIR and NIR
pictures should help identifying such objects.

Warm certainly enough to maybe melt water depending on how slowly it
spins - that is why comets develop tails as they near the sun.

However a perfect black body at the Earth's orbit without an atmosphere
their peak sun side temperature is likely to be more like 5C peaking at
around 12um. Enough that the more sensitive far IR systems might see it.
How bright the side facing Earth is depends on its actual temperature
which could be quite a bit cooler.

There was never enough military demand to see objects cooler than 37C so
the sensitivity is not so good at these longer thermal wavelengths.

Since the hot object is tumbling around it will also radiate ThIR on
the "night" side of the object, while a very reflective object nearly
on the line between Sun and Earth, will have a very small reflective
area for visible light and NIR.

I think most of the survey instruments are wide field big sensor devices
on fast Schmidt scopes mostly in the visible or near IR backed with
computer programs to spot anything that moves.

--
Regards,
Martin Brown

 

On Wed, 31 Jul 2019 13:07:21 +0100, Martin Brown
<'''newspam'''@nezumi.demon.co.uk> wrote:

On 31/07/2019 07:20, upsidedown@downunder.com wrote:
On Tue, 30 Jul 2019 22:51:24 +0100, Martin Brown
'''newspam'''@nezumi.demon.co.uk> wrote:

On 29/07/2019 17:42, upsidedown@downunder.com wrote:
On Mon, 29 Jul 2019 00:21:56 GMT, Steve Wilson <no@spam.com> wrote:

July 26, 2019

How Astronomers Missed the Massive Asteroid That Just Whizzed Past Earth

By Yasemin Saplakoglu, Staff Writer

A large asteroid just whizzed past our planet - and astronomers
weren't expecting it.

Ranging in size from 187 to 427 feet (57 to 130 meters) wide, the
space rock named 2019 OK snuck up on us Thursday morning (July 25).

It swung as close as 45,000 miles (73,000 kilometers) from Earth,
what one astronomer told The Washington Post was "uncomfortably
close."

Some animation claim that the flyby occurred when the asteroid was
flying towards perihelion, i.e. it would come from the night side of
Earth and it should be easier to detect earlier.

The big ones that sneak up on us are typically either very dark covered
in carbon soot like dust or coming from the direction of the sun so that
they are in the twilight sky until the last possible moment or both. I
am a bit surprised that the automatic searchers didn't get it a bit
sooner (so will they be). There is a protocol for Earth crossers with
suspected close approach or collision risk at the minor planets centre.

A very dark carbon asteroid inside the orbit of the Earth will get
*hot* and radiate a lot in the 8-15 um thermal-IR range but very
little in the near-IR or visible range. Thus comparing ThIR and NIR
pictures should help identifying such objects.

Warm certainly enough to maybe melt water depending on how slowly it
spins - that is why comets develop tails as they near the sun.

That is more about sublimation (going directly from solid to gas).

However a perfect black body at the Earth's orbit without an atmosphere
their peak sun side temperature is likely to be more like 5C peaking at
around 12um.

The average full sphere temperature would be close to -15 C. However,
for "equatorial" regions the variation can be quite large. Look at the
day time surface temperatures of the Moon, it can be uncomfortably
high. Admittedly the sun has been shining for up to two weeks. Anyway
for faster rotating bodies the warm equatorial regions going from late
"evening" to early "night" is still quite warm and radiates ThIR quite
well.

Enough that the more sensitive far IR systems might see it.
How bright the side facing Earth is depends on its actual temperature
which could be quite a bit cooler.

There was never enough military demand to see objects cooler than 37C so
the sensitivity is not so good at these longer thermal wavelengths.

Since the hot object is tumbling around it will also radiate ThIR on
the "night" side of the object, while a very reflective object nearly
on the line between Sun and Earth, will have a very small reflective
area for visible light and NIR.

I think most of the survey instruments are wide field big sensor devices
on fast Schmidt scopes mostly in the visible or near IR backed with
computer programs to spot anything that moves.

The most sensitive IR detectors are cooled by letting helium evaporate
at 4 K. This unfortunately means that the detector is usable only as
long as there is some liquid helium left in the tanks.

 

[Rick C]

On Wednesday, July 31, 2019 at 9:30:44 AM UTC-4, upsid...@downunder.com wrote:

On Wed, 31 Jul 2019 13:07:21 +0100, Martin Brown
'''newspam'''@nezumi.demon.co.uk> wrote:

On 31/07/2019 07:20, upsidedown@downunder.com wrote:
On Tue, 30 Jul 2019 22:51:24 +0100, Martin Brown
'''newspam'''@nezumi.demon.co.uk> wrote:

On 29/07/2019 17:42, upsidedown@downunder.com wrote:
On Mon, 29 Jul 2019 00:21:56 GMT, Steve Wilson <no@spam.com> wrote:

July 26, 2019

How Astronomers Missed the Massive Asteroid That Just Whizzed Past Earth

By Yasemin Saplakoglu, Staff Writer

A large asteroid just whizzed past our planet - and astronomers
weren't expecting it.

Ranging in size from 187 to 427 feet (57 to 130 meters) wide, the
space rock named 2019 OK snuck up on us Thursday morning (July 25).

It swung as close as 45,000 miles (73,000 kilometers) from Earth,
what one astronomer told The Washington Post was "uncomfortably
close."

Some animation claim that the flyby occurred when the asteroid was
flying towards perihelion, i.e. it would come from the night side of
Earth and it should be easier to detect earlier.

The big ones that sneak up on us are typically either very dark covered
in carbon soot like dust or coming from the direction of the sun so that
they are in the twilight sky until the last possible moment or both. I
am a bit surprised that the automatic searchers didn't get it a bit
sooner (so will they be). There is a protocol for Earth crossers with
suspected close approach or collision risk at the minor planets centre.

A very dark carbon asteroid inside the orbit of the Earth will get
*hot* and radiate a lot in the 8-15 um thermal-IR range but very
little in the near-IR or visible range. Thus comparing ThIR and NIR
pictures should help identifying such objects.

Warm certainly enough to maybe melt water depending on how slowly it
spins - that is why comets develop tails as they near the sun.

That is more about sublimation (going directly from solid to gas).


However a perfect black body at the Earth's orbit without an atmosphere
their peak sun side temperature is likely to be more like 5C peaking at
around 12um.

The average full sphere temperature would be close to -15 C. However,
for "equatorial" regions the variation can be quite large. Look at the
day time surface temperatures of the Moon, it can be uncomfortably
high. Admittedly the sun has been shining for up to two weeks. Anyway
for faster rotating bodies the warm equatorial regions going from late
"evening" to early "night" is still quite warm and radiates ThIR quite
well.

Enough that the more sensitive far IR systems might see it.
How bright the side facing Earth is depends on its actual temperature
which could be quite a bit cooler.

There was never enough military demand to see objects cooler than 37C so
the sensitivity is not so good at these longer thermal wavelengths.

Since the hot object is tumbling around it will also radiate ThIR on
the "night" side of the object, while a very reflective object nearly
on the line between Sun and Earth, will have a very small reflective
area for visible light and NIR.

I think most of the survey instruments are wide field big sensor devices
on fast Schmidt scopes mostly in the visible or near IR backed with
computer programs to spot anything that moves.

The most sensitive IR detectors are cooled by letting helium evaporate
at 4 K. This unfortunately means that the detector is usable only as
long as there is some liquid helium left in the tanks.

Isn't the temperature of space below that? So a shielded radiator should be able to dissipate the heat absorbed by the satellite and condense the helium. The helium would then be essentially a heat pipe. This may be too large to be practically launched.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

 

[Martin Brown]

On 31/07/2019 19:54, Rick C wrote:

On Wednesday, July 31, 2019 at 9:30:44 AM UTC-4,
upsid...@downunder.com wrote:
On Wed, 31 Jul 2019 13:07:21 +0100, Martin Brown
'''newspam'''@nezumi.demon.co.uk> wrote:

On 31/07/2019 07:20, upsidedown@downunder.com wrote:
On Tue, 30 Jul 2019 22:51:24 +0100, Martin Brown
'''newspam'''@nezumi.demon.co.uk> wrote:

On 29/07/2019 17:42, upsidedown@downunder.com wrote:
On Mon, 29 Jul 2019 00:21:56 GMT, Steve Wilson
no@spam.com> wrote:

July 26, 2019

How Astronomers Missed the Massive Asteroid That Just
Whizzed Past Earth

By Yasemin Saplakoglu, Staff Writer

A large asteroid just whizzed past our planet - and
astronomers weren't expecting it.

Ranging in size from 187 to 427 feet (57 to 130 meters)
wide, the space rock named 2019 OK snuck up on us
Thursday morning (July 25).

It swung as close as 45,000 miles (73,000 kilometers)
from Earth, what one astronomer told The Washington Post
was "uncomfortably close."

Some animation claim that the flyby occurred when the
asteroid was flying towards perihelion, i.e. it would come
from the night side of Earth and it should be easier to
detect earlier.

The big ones that sneak up on us are typically either very
dark covered in carbon soot like dust or coming from the
direction of the sun so that they are in the twilight sky
until the last possible moment or both. I am a bit surprised
that the automatic searchers didn't get it a bit sooner (so
will they be). There is a protocol for Earth crossers with
suspected close approach or collision risk at the minor
planets centre.

A very dark carbon asteroid inside the orbit of the Earth will
get *hot* and radiate a lot in the 8-15 um thermal-IR range but
very little in the near-IR or visible range. Thus comparing
ThIR and NIR pictures should help identifying such objects.

Warm certainly enough to maybe melt water depending on how slowly
it spins - that is why comets develop tails as they near the
sun.

That is more about sublimation (going directly from solid to gas).


However a perfect black body at the Earth's orbit without an
atmosphere their peak sun side temperature is likely to be more
like 5C peaking at around 12um.

The average full sphere temperature would be close to -15 C.
However, for "equatorial" regions the variation can be quite large.
Look at the day time surface temperatures of the Moon, it can be
uncomfortably high. Admittedly the sun has been shining for up to
two weeks. Anyway for faster rotating bodies the warm equatorial
regions going from late "evening" to early "night" is still quite
warm and radiates ThIR quite well.

Enough that the more sensitive far IR systems might see it. How
bright the side facing Earth is depends on its actual
temperature which could be quite a bit cooler.

There was never enough military demand to see objects cooler than
37C so the sensitivity is not so good at these longer thermal
wavelengths.

Since the hot object is tumbling around it will also radiate
ThIR on the "night" side of the object, while a very reflective
object nearly on the line between Sun and Earth, will have a
very small reflective area for visible light and NIR.

I think most of the survey instruments are wide field big sensor
devices on fast Schmidt scopes mostly in the visible or near IR
backed with computer programs to spot anything that moves.

The most sensitive IR detectors are cooled by letting helium
evaporate at 4 K. This unfortunately means that the detector is
usable only as long as there is some liquid helium left in the
tanks.

Isn't the temperature of space below that? So a shielded radiator
should be able to dissipate the heat absorbed by the satellite and
condense the helium. The helium would then be essentially a heat
pipe. This may be too large to be practically launched.

It is very difficult to do that. The standard tricks get you a heat
shadow. The Hubble ran into a bunch of related problems with thermal
effects known to the spook bird manufacturers but highly classified.
They had to reinvent the wheel (and theirs was a bit rounder too).

Sticking a mirror or maybe two in the path between the sun and the
sensor is about as good as you can get. Biggest problem is that for a
wide angle survey instrument you want a very large number of pixels.

So instead of 0.01 radian diameter source at 5800K and the rest at 4K
you trade that for 0.05 radian occulting disk at 280K emitting maybe
5-10% and the rest at 4K with one good mirror interposed. Two is about
where the law of diminishing returns sets in.

In low Earth orbit you also have a hefty chunk of 300K emission very
nearby and subtending a much larger solid angle than the sun.

--
Regards,
Martin Brown

 

>Isn't the temperature of space below that?

Temperature is a property of matter.

 

[Bert Timmerman]

Steve Wilson wrote:

July 26, 2019

How Astronomers Missed the Massive Asteroid That Just Whizzed Past Earth

By Yasemin Saplakoglu, Staff Writer

A large asteroid just whizzed past our planet - and astronomers
weren't expecting it.

Ranging in size from 187 to 427 feet (57 to 130 meters) wide, the
space rock named 2019 OK snuck up on us Thursday morning (July 25).

It swung as close as 45,000 miles (73,000 kilometers) from Earth,
what one astronomer told The Washington Post was "uncomfortably
close."

If the asteroid had actually collided with Earth, the crash would
have caused devastating damage.

For example, back in 2013, a meteor snuck up on us and exploded over
the Russian city of Chelyabinsk; that blast was stronger than a
nuclear explosion, and the resulting shock wave shattered glass down
below and injured more than 1,000 people. The Chelyabinsk meteor was
much smaller than 2019 OK, spanning about 66 feet (20 meters)
across.

NASA is tracking over 90 percent of the asteroids that are 0.62
miles (1 km) or larger and are orbiting close to our planet.

https://www.livescience.com/66043-giant-asteroid-flyby-surprises-
astronomers.html
----------------------------------------------------------------

Pleasant dreams

Hrmmm, Looks like we're spending all those trillions on the "wrong" type
of defense industry LOL ;-)

Let's see if we can get the elevators working on the "Gerald".

 

[Jeroen Belleman]

Bert Timmerman wrote:

Steve Wilson wrote:
July 26, 2019

How Astronomers Missed the Massive Asteroid That Just Whizzed Past Earth

By Yasemin Saplakoglu, Staff Writer

A large asteroid just whizzed past our planet - and astronomers
weren't expecting it.
[...]

Pleasant dreams

Hrmmm, Looks like we're spending all those trillions on the "wrong" type
of defense industry LOL ;-)

You're a good deal more likely to be killed in a war
than by a falling asteroid.

Jeroen Belleman

 

[John Miles, KE5FX]

On Tuesday, July 30, 2019 at 7:13:11 AM UTC-7, bitrex wrote:

the headline says "massive" but asteroids at the lower end of that range
are small enough that if you could intercept exoatmospherically with a
ten, 20 megaton nuclear weapon at a couple hundred meters would vaporize
the bulk of it.

Problem: Huge-ass asteroid on collision course with Earth

Solution: Nuke it

Problem: 12 medium-sized radioactive asteroids on collision course with Earth

-- john, KE5FX

 

[Bill Sloman]

On Thursday, August 1, 2019 at 9:13:03 PM UTC+10, John Miles, KE5FX wrote:

On Tuesday, July 30, 2019 at 7:13:11 AM UTC-7, bitrex wrote:
the headline says "massive" but asteroids at the lower end of that range
are small enough that if you could intercept exoatmospherically with a
ten, 20 megaton nuclear weapon at a couple hundred meters would vaporize
the bulk of it.

Problem: Huge-ass asteroid on collision course with Earth

Solution: Nuke it

Problem: 12 medium-sized radioactive asteroids on collision course with Earth

If you use a big enough nuke, the fragments will all have been moved onto slightly different orbits - if they are all moving apart, none of them are on the original orbit.

Even if you don't blast it into separate bits, what you do blast off will have momentum in a different direction to what's left of the asteroid, and the residue will have an equal and opposite change of momentum.

It's all calculable - more accurately after the blast - and if a first blast didn't do all that was needed, you'll probably have time for another.

--
Bill Sloman, Sydney

 

[Martin Brown]

On 01/08/2019 05:49, jurb6006@gmail.com wrote:

Isn't the temperature of space below that?

Temperature is a property of matter.

The vacuum of space isn't a perfect vacuum though so it has a poorly
defined temperature - there is always some matter present no matter how
tenuous. You can get weird results though when the distribution of
particle speeds is nothing like thermal for example in the solar wind.

It is also a property of the now very distant surface of last scattering
of the universe in the form of the microwave background from the moment
when the previously ionised plasma universe recombined to neutral
hydrogen and became transparent to electromagnetic radiation.

Presently after red shifting that looks like about 2.7K from Earth.

https://en.wikipedia.org/wiki/Cosmic_microwave_background


--
Regards,
Martin Brown