PSU: Nearby planetary system mystery solved

[MargaritaMc]

Mysteries of a nearby planetary system's dynamics now are solved
... Numerous studies since 2002 had failed to determine a plausible model for the masses and orbits of two giant planets located closer to 55 Cancri than Mercury is to our Sun. Astronomers had struggled to understand how these massive planets orbiting so close to their star could avoid a catastrophe such as one planet being flung into the star, or the two planets colliding with each other. Now, the new study led by Penn State has combined thousands of observations with new statistical and computational techniques to measure the planets' properties more accurately, revealing that their particular masses and orbits are preventing the system from self-destructing anytime soon. ...
More info at
http://www.eurekalert.org/pub_releases/ ... 041514.php

http://arxiv.org/abs/1402.6343The 55 Cancri Planetary System: Fully Self-Consistent N-body Constraints and a Dynamical Analysis

Benjamin E. Nelson, Eric B. Ford, Jason T. Wright, Debra A. Fischer, Kasper von Braun, Andrew W. Howard, Matthew J. Payne, Saleh Dindar

[MargaritaMc]

I emailed Eric Ford at Penn State about this part of the press release

"It was only in 2011, 8 years after the discovery of this inner-most planet (55 Cnc e) that astronomers recognized it orbited its host star in less than 18 hours, rather than nearly 3 days, as originally thought.

Soon after, astronomers detected the shadow of the planet passing over the Earth, allowing astronomers to measure the size of the planet relative to the size of the star."

as I assumed that "Earth" was a typo.

But he has replied and said that that was exactly what was meant, that the Kepler observatory detects the shadow of an Earth-size planet hundreds of light years away passing over us. Or rather, that the Kepler spacecraft, detects the shadow passing over it, but it's relatively close to Earth in astronomical distance scales.

Can anyone explain what this means?!

[BMAONE23]

I would imagine that the "Shadow" referenced is the apparent dimming of the host star brightness.

[geckzilla]

The first time I heard the word shadow used like that was for that Regulus occultation that not a single person was able to witness. When you think about it, yeah, those teeny weeny little blips are definitely shadows. It's funny to think that a planet light years away is casting a shadow on Earth and yet it must for us to detect its star dimming.

[BDanielMayfield]

Think of the umbra and penumbra in eclipses. One is full coverage, dark shadow, while the other is only partial, but they are both shadows.

PS: Don't ask me which is which though. My knowledge is only partial.

[Nitpicker]

Think of the umbra and penumbra in eclipses. One is full coverage, dark shadow, while the other is only partial, but they are both shadows.

PS: Don't asks me which is which though. My knowledge is only partial.

Nah. The distant star is an unresolved point source of light and the distant planet an unresolved "shadow" (or reduction) in the light signal obtained from the star. Umbral and penumbral shadows are normally terms used in the context of astronomical objects which are resolvable into discs. (I suppose that if the signal is diminished, we could say that we are in the planet's penumbral shadow with respect to its star, but it gets a bit silly when you realise that the planets in this case -- orbiting 55 Cnc A -- cast their shadows about 41 years before we observed them.)

[BDanielMayfield]

You labeled yourself well Nitpicker, but it's all good. My knowledge is now less partial.

[Nitpicker]

You labeled yourself well Nitpicker, but it's all good. My knowledge is now less partial.

You were not wrong. I just don't think the terms umbra and penumbra are particularly "illuminating" in explaining the reality of this kind of shadowy observation.

[BMAONE23]

Think of the umbra and penumbra in eclipses. One is full coverage, dark shadow, while the other is only partial, but they are both shadows.

PS: Don't asks me which is which though. My knowledge is only partial.

I am often finding my astronomy knowledge eclipsed by others that post here as well

[Chris Peterson]

The distant star is an unresolved point source of light and the distant planet an unresolved "shadow" (or reduction) in the light signal obtained from the star. Umbral and penumbral shadows are normally terms used in the context of astronomical objects which are resolvable into discs. (I suppose that if the signal is diminished, we could say that we are in the planet's penumbral shadow with respect to its star, but it gets a bit silly when you realise that the planets in this case -- orbiting 55 Cnc A -- cast their shadows about 41 years before we observed them.)

What's silly about it?

We are in the penumbral (or antumbral) shadow when we observe any transit (which is the case with Kepler), and we're in the umbral shadow when we observe any occultation (such as when an asteroid passes in front of a star). Whether the star or the occulting/transiting body are resolvable or not is completely irrelevant, as is the light travel time between the event and the observation.

[MargaritaMc]

I asked Ben Nelson, the first named author, on his blog. His reply is here:
http://qdelmine.blogspot.com.es/2014/04 ... 3032921491

Oh, and the Kepler telescope wasn't involved! Dr Ford must have made a typo in his email to me.
M

[Nitpicker]

What's silly about it?

We are in the penumbral (or antumbral) shadow when we observe any transit (which is the case with Kepler), and we're in the umbral shadow when we observe any occultation (such as when an asteroid passes in front of a star). Whether the star or the occulting/transiting body are resolvable or not is completely irrelevant, as is the light travel time between the event and the observation.

It seems that the only silly thing is my own bias as it pertains to the application of the terms umbral, penumbral and antumbral. They would appear commonly to have a wider application. My apologies to all involved.

[MargaritaMc]

There is an article in Sky and Telescope about this research.

M