**CHALLENGE QUESTION**
Mars has two moons: Phobos and Deimos.Let us say that at their closet approach, Phobos is **14,235.9 kilometers from Deimos**. Phobos has a **radius of 11.1** kilometers, and Deimos has an arc measurement of about **17.97 arcseconds**.
Given these values:
* Estimate the **diameter** of Deimos in km,
* Estimate the **Arc measurement (in arcminutes)** of Phobos as viewed from Deimos.
ESA’s Mars Express orbiter imaged the martian moons Phobos and Deimos together on 5 November 2009.