Discovery of non-transiting exo planets possible?

[David Spain]

Kepler uses dip in light curves of stars to determine the existence of
exo-planets, but that presumption is that these "exo" solar systems have
their ecliptics aligned with us so that transits are observable, but
there must be far more systems that do not fit that criterion than do.

So are there any telescopes in the works that can not only detect
reflected light from exo-planets but can use light arcs around their
home stars to detect them?

Just curious.

[Gary Harnagel]

Post by David Spain
Kepler uses dip in light curves of stars to determine the existence of
exo-planets, but that presumption is that these "exo" solar systems have
their ecliptics aligned with us so that transits are observable, but
there must be far more systems that do not fit that criterion than do.
So are there any telescopes in the works that can not only detect
reflected light from exo-planets but can use light arcs around their
home stars to detect them?
Just curious.

Several exoplanets have been discovered by other means, the latest being
one orbiting Proxima Centauri:

https://en.wikipedia.org/wiki/Proxima_Centauri#Planetary_system

[[Mod. note -- To answer answer to the poster's original question:

No current telescope can directly resolve the "light arc" produced when
an extrasolar planet acts as a gravitational lens for a background star.
But this phenomenon also *brightens* the background star, and this
brightening is detectable. A number of extrasolar planets have in fact
been discovered via this "microlensing" technique:
https://en.wikipedia.org/wiki/Gravitational_microlensing#Detection_of_extrasolar_planets
-- jt]]

[John Heath]

Post by David Spain
Kepler uses dip in light curves of stars to determine the existence of
exo-planets, but that presumption is that these "exo" solar systems have=
their ecliptics aligned with us so that transits are observable, but
there must be far more systems that do not fit that criterion than do.
So are there any telescopes in the works that can not only detect
reflected light from exo-planets but can use light arcs around their
home stars to detect them?
Just curious.

Our planets rotate on the similar plain to our galaxy. Lets call
the odds of most of our planets orbiting on the same plain as our
galaxy 50 to 1 , ruff estimate. This would mean that the odds of
other solar systems in our galaxy also being on the same plain as
our galaxy high. This improves the possibility of sensing a dip in
brightness caused by a planet in front of it's star if the telescope
is pointed in the direction of our galaxy on the same plain.

However the arcs would be nice. I would venture a guess the planet
reflected light is too small and added to this being very close to
a bright star. It would exceed the dynamic range of the light sensor.
A 16 bit A/D would have a hard time telling the difference between
a bright star and a dim planet.

[[Mod. note --
1. No, the planets in our solar system do NOT orbit in the plane of
our galaxy.
2. The author is correct that directly imaging an extrasolar planet
requires a HUGE dynamic range. To this end, attempts to do this
generally include a coronagraph to block almost all of the host
star's light. There's a bit of discussion of coronagraph designs
in Wikipedia:
https://en.wikipedia.org/wiki/Coronagraph
Even with a coronagraph, scattered light from the host star is
still the #1 problem in direct detection of extrasolar planets.
-- jt]]

[Phillip Helbig (undress to reply)]

Post by John Heath

Kepler uses dip in light curves of stars to determine the existence of=
exo-planets, but that presumption is that these "exo" solar systems hav=

e

Post by John Heath

their ecliptics aligned with us so that transits are observable, but
there must be far more systems that do not fit that criterion than do.
So are there any telescopes in the works that can not only detect
reflected light from exo-planets but can use light arcs around their
home stars to detect them?
Just curious.

Our planets rotate on the similar plain to our galaxy.

Nope. If so, the Milky Way would lie along the ecliptic. It's almost
perpendicular to it. Sometimes you can discover interesting stuff by
just looking at the sky. :-)

[Steve Willner]

Post by Gary Harnagel
[[Mod. note --
1. No, the planets in our solar system do NOT orbit in the plane of
our galaxy.

Indeed: the Galactic latitude of the north ecliptic pole is about
29.8 deg. It would be 90 deg if the two planes were aligned.

Post by Gary Harnagel
2. The author is correct that directly imaging an extrasolar planet
requires a HUGE dynamic range. To this end, attempts to do this
generally include a coronagraph to block almost all of the host
star's light. There's a bit of discussion of coronagraph designs
https://en.wikipedia.org/wiki/Coronagraph
Even with a coronagraph, scattered light from the host star is
still the #1 problem in direct detection of extrasolar planets.
-- jt]]

Nevertheless, planets have been directly detected in a few systems.
I _think_ the first was beta Pictoris (Lagrange et al. 2010):
http://science.sciencemag.org/content/329/5987/57.full

HR 8799 shows three planets (Marois et al. 2010):
http://www.nature.com/articles/nature09684

There are other examples; those are just two I happened to find.

A recent article by Meshkat et al. (2017)
http://iopscience.iop.org/article/10.3847/1538-3881/aa8e9a/meta
reports a systematic but unsuccessful search of stars known to have
debris disks. Their Introduction gives references to prior
successful imaging studies.

[David Spain]

Post by David Spain
So are there any telescopes in the works that can not only detect
reflected light from exo-planets but can use light arcs around their
home stars to detect them?
Just curious.

Well to be honest I was thinking in terms of "arcs" of reflected light
off a resolved planet more or less acting as a point of light that would
be seen over a long duration plot to detect orbital travel. I wasn't
thinking in terms of gravitational lensing at all. But of course that
might be a better way to go if you don't have the dynamic range to
detect such faint images.

Will the Webb telescope provide any additional capabilities in this
area? Forgive the naive question, astronomy is my hobby not my profession.

David Spain

[Steve Willner]

Post by David Spain
I was thinking in terms of "arcs" of reflected light
off a resolved planet more or less acting as a point of light that would
be seen over a long duration plot to detect orbital travel.

Exposure times are short compared to orbit times, so when planets are
directly imaged, they show up as point sources. My previous message
gave some examples, and the Introduction section in the Meshkat
article gives references to others.

Post by David Spain
I wasn't thinking in terms of gravitational lensing at all. But of
course that might be a better way to go if you don't have the
dynamic range to detect such faint images.

The idea is that when a foreground star lenses a background one, if
the foreground star has a planet, it can add to the lensing
signal. The timescale is much shorter, though, because the planet's
mass is much smaller than the star's mass. You might do web searches
on "Einstein radius" and on "microlensing."

Post by David Spain
Will the Webb telescope provide any additional capabilities in this
area?

The Near Infrared Camera has a coronagraph, which is intended to
block light from the star and allow planets to be imaged. (The
coronagraph has uses for other projects as well.) Together with the
large telescope aperture, which gives high angular resolution, it
should be possible to image planets much closer to their primary
stars than can be done now. Of course the planets have to be there
and be either large and shiny or large and hot, but there should be
some very nice images coming. I see there is one Early Release
Science project that includes imaging of one exoplanet:
https://jwst.stsci.edu/files/live/sites/jwst/files/home/news/_documents/ers-1386-hinkley.pdf
The main goal of this project is to test the instrument; I'm sure
there will be more projects done.