near as I can tell, this is the relevant trait:
<Trait>
<InternalName>OutreachTrait5</InternalName>
<DisplayName>OutreachTrait5_Name</DisplayName>
<ShortDescription>OutreachTrait5_ShortDec</ShortDescription>
<Description>OutreachTrait5_Dec</Description>
<Icon>Outreach5_Hot.png</Icon>
<DisabledIcon>Outreach5_Disabled.png</DisabledIcon>
<CultureCost>15</CultureCost>
<AICategoryWeight>
<Military>3</Military>
<Growth>9</Growth>
<Tech>4</Tech>
<Diplomacy>2</Diplomacy>
<Expansion>10</Expansion>
<Wealth>5</Wealth>
<Influence>7</Influence>
<Fortification>6</Fortification>
</AICategoryWeight>
<Triggers>
<OnEvent>OnCultureTraitUnlock</OnEvent>
<PerformAction>
<Action>DiscoverNearbyPlanetOfClass</Action>
<ValueParam>10</ValueParam>
<StringParam>DiscoveredWorldPlanetTrait</StringParam>
<StringParam>OUTREACH5_POPUP_MESSAGE</StringParam>
</PerformAction>
</Triggers>
</Trait>
and just to clear up doubt
<StringTable>
<Label>OutreachTrait5_ShortDec</Label>
<String>Grants a class 16 planet.</String>
</StringTable>
<StringTable>
<Label>OutreachTrait5_Dec</Label>
<String>A reclusive world, long hidden from the rest of the galaxy, has decided that our civilization is a beacon of enlightenment, and worth alligning itself with.</String>
</StringTable>
I'm not sure how it comes with a class 8 or class 16 but suspect something might be adding an extra variable (?)