title: wrong number of lifetime parameters: expected 1, found 0
body: <p>I'm having a really hard time fathoming pointers in Rust. This code won't compile because: <code>wrong number of lifetime parameters: expected 1, found 0 [E0107]</code>. What does that mean?</p>
  
  <pre><code>struct Planet&lt;'a&gt; {
      name: &amp;'a str,
      radius_km: i32,
      surface_area_km2: i64,
      orbital_period_days: i32,
      distance_from_sun: i64
  }
  
  fn mercury() -&gt; Planet {
      Planet {
          name: "Mercury",
          radius_km: 2_440,
          surface_area_km2: 74_800_000,
          orbital_period_days: 88,
          distance_from_sun: 57_910_000
      }
  }
  
  fn main() {
      let mercury = Box::new(mercury());
      println!("{}",mercury.name)
  }
  </code></pre>