Lord Dover
We are conducting an observing campaign with a sample of near-Earth asteroids (NEAs) to detect YORP-induced acceleration. Photometric lightcurves from small to medium optical telescopes are used to detect changes to spin state. Where available, radar and thermal-IR observations are used to develop physical models that are used to determine expected YORP strengths. We present the results of an analysis of 2000 PN9 using optical and radar observations between 2001 and 2016. A detailed physical model has been developed to describe the shape and spin-state of the asteroid. PN9 is top-shaped with an equatorial ridge, and is rotating close to the spin-breakup limit. PN9 is the largest asteroid known to have this distinctive and highly symmetrical 'YORPoid' shape, and is the fastest-rotating top-shaped body that is not part of a multiple system. Due to the size and shape of PN9, an observational detection of YORP acceleration has not been possible with the available data. The shape and rotation period indicate that PN9 is a YORP-evolved body similar to 1999 KW4, and that it is a good candidate for future detection of mass-lofting events.
This introductory slide contains a text box proving a brief description of the YORP effect and the analysis we have conducted.
An image shows a computer generated wire-frame model of the asteroid 2000 PN9. The asteroid is shaped like a slightly squashed ball, with a flattened top and bottom. Halfway down the asteroid, where it is widest, there is a small but sharp ridge going all the way around the asteroid.
Slide 2
This slide is broken into two sides. On the left, Figure 1 shows a graph with the periodic solar phase angle (0 to 150 degrees) against time (2000 to 2021). Red crosses mark three dates for radar observations in 2001 and two in 2006. Blue circles represent dates for optical observations in 2006, 2010, 2015, 2016 and 2020. Below this description are bulletpoints summarising these datapoints and there is a link to view a Google spreadsheet containing a full list of observations.
On the right hand side of slide 2 there is a brief summary of the process for developing a physical model. Below this summary, Figure 2 shows three images, each of which is comprised of three panels.
In each image, the first panel shows a delay-Doppler image, showing a slightly asymmetrical arc. The second panel shows the corresponding synthetic delay-Doppler image, which closely matches the appearance of the first panel (albeit with no noise). The third panel shows the plane-of-sky view, where our shape model - described in slide one - is oriented and rotated to show the face that it presents to Earth for the corresponding delay-Doppler image. Each image is labelled with a date and observatory: Goldstone on 2001-03-03 and 2006-03-07, and Arecibo on 2001-03-05. For each of these three dates, the delay-Doppler images show slightly different shapes and the plane-of-sky views show a different view of the asteroid.
It is important to understand that in delay-Doppler images, the observer is viewing from the top of the image. The vertical axis shows delay, thus the closest part of the asteroid is at the top and the farthest is at the bottom. The horizontal axis represents Doppler shift, so signal on the left hand size is returned from a surface moving away from the Earth. Signal on the right hand side is thus reflected from a surface moving towards the Earth. Information on three-dimensional shape is condensed to two dimensions, making if difficult for the untrained eye to recognise how the plane-of-sky view could result in the corresponding delay-Doppler image.
Each of these images can be clicked on to view animations of the delay-Doppler images and plane-of-sky views as the asteroid rotates (these launch in an external webpage).
Slide 3
A text box discusses the results of our analysis. On the left, a table lists parameters of our shape model. On the right, Figure 3 is an image constructed of six panels. These panels show our shape model from the top, the bottom, and the four sides, with respect to the rotation axis.
Slide 4
Two sets of bulletpoints describe our conclusions and future work.
Below these are boxes containing Acknowledgements and References.
If you would like me to send you text or other information from the poster, or have any questions, you can email me at lrd27@kent.ac.uk