Please read the following table in HTML format from a webpage and then answer the question in detail according to the table. Each table cell is defined by a <td> and a </td> tag. Each table row starts with a <tr> and ends with a </tr> tag. 'rowspan=m' and 'colspan=n' represents a cell spaning over 'm' rows and 'n' columns.

Webpage title:
Planets beyond Neptune
Table title:
Pluto loses Planet X title
Table:
<table id='hittask' contenteditable='False'>
<tr> <th colspan=1 rowspan=1 > Year </th><th colspan=1 rowspan=1 > Mass </th><th colspan=1 rowspan=1 > Notes </th></tr>
<tr> <td class="highlighted"  colspan=1 rowspan=1 > 1931 </td><td colspan=1 rowspan=1 > 1 Earth </td><td class="highlighted"  colspan=1 rowspan=1 > Nicholson & Mayall </td></tr>
<tr> <td class="highlighted"  colspan=1 rowspan=1 > 1942 </td><td class="highlighted"  colspan=1 rowspan=1 > 0.91 Earth </td><td class="highlighted"  colspan=1 rowspan=1 > Wylie </td></tr>
<tr> <td colspan=1 rowspan=1 > 1948 </td><td colspan=1 rowspan=1 > 0.1 (1/10 Earth) </td><td colspan=1 rowspan=1 > Kuiper </td></tr>
<tr> <td colspan=1 rowspan=1 > 1973 </td><td colspan=1 rowspan=1 > 0.025 (1/40 Earth) </td><td colspan=1 rowspan=1 > Rawlins </td></tr>
<tr> <td colspan=1 rowspan=1 > 1976 </td><td colspan=1 rowspan=1 > 0.01 (1/100 Earth) </td><td colspan=1 rowspan=1 > Cruikshank, Pilcher, & Morrison </td></tr>
<tr> <td colspan=1 rowspan=1 > 1978 </td><td colspan=1 rowspan=1 > 0.002 (1/500 Earth) </td><td colspan=1 rowspan=1 > Christy & Harrington </td></tr>
<tr> <td colspan=1 rowspan=1 > 2006 </td><td colspan=1 rowspan=1 > 0.00218 (1/459 Earth) </td><td colspan=1 rowspan=1 > Buie et al. </td></tr>
</table>
Question:
What were the earliest measurements of the mass of Neptune?
Answer:
In 1931, Nicholson and Mayall calculated Neptune's mass to be equal to 1 Earth, a value similar to the 0.91 Earth mass calculated in 1942 by Lloyd R. Wylie.